Optical element and exposure apparatus

ABSTRACT

An optical element is used for an exposure apparatus which is configured to illuminate a mask with an exposure light beam for transferring a pattern on the mask onto a substrate through a projection optical system and to interpose a given liquid in a space between a surface of the substrate and the projection optical system. The optical element includes a first anti-dissolution member provided on a surface of a transmissive optical element on the substrate&#39;s side of the projection optical system.

This is a Divisional of application Ser. No. 10/569,207 filed Feb. 23,2006, which in turn is a National Stage of PCT/JP2004/012296, filed Aug.26, 2004. The disclosure of the prior applications are herebyincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present invention relates to an optical element used in a projectionexposure apparatus adopting the liquid immersion method, which isapplied to the lithography step for transferring a mask pattern onto aphotosensitive substrate to produce devices including, for example,semiconductor elements, image pickup devices (such as CCDs), liquidcrystal display elements, and thin film magnetic heads. The presentinvention also relates to an exposure apparatus applying the opticalelement.

BACKGROUND ART

A projection exposure apparatus configured to transfer a pattern imageof a reticle as a mask onto each shot area on a resist-coated wafer (ora glass plate and so forth) serving as a photosensitive substratethrough a projection optical system is used for manufacturingsemiconductor elements and the like. A reduced projection type exposureapparatus (a stepper) applying a step and repeat method has beenconventionally used as the projection exposure apparatus in many cases.Meanwhile, a projection exposure apparatus applying a step-and-scanmethod configured to scan and expose the reticle and the wafersynchronously is also drawing attentions in these days.

Resolution of the projection optical system incorporated in theprojection exposure apparatus becomes higher as an exposure wavelengthused therein becomes shorter or as the numerical aperture of theprojection optical system becomes larger. Therefore, the exposurewavelength used in the projection exposure apparatus is becoming shorterevery year while the numerical aperture of the projection optical systemis gradually increasing along developments in finer process rules formanufacturing integrated circuits. Although the dominant exposurewavelength today is 248 nm of a KrF excimer laser, an ArF excimer laserhaving a shorter exposure wavelength of 193 nm is also being put intopractical use recently.

Incidentally, along the reduction in the wavelength of exposure light,types of glass materials having sufficient optical transmittance forobtaining light intensity required for exposure while ensuring a desiredimage-forming performance are limited. In this context, there isdisclosed a projection exposure apparatus of a liquid immersion typeconfigured to fill a space between a lower surface of a projectionoptical system and a surface of a wafer with a liquid such as water oran organic solvent, and to improve resolution by utilizing a phenomenonthat the wavelength of exposure light in liquid becomes 1/n (n denotes arefractive index of liquid usually ranging from about 1.2 to 1.6) timesas large as the wavelength in the air (Japanese Patent ApplicationLaid-Open Gazette No. Hei 10-303114 (JP 10-303114 A)).

DISCLOSURE OF THE INVENTION

The projection optical system contacts the liquid when configuring thisprojection exposure apparatus of the liquid immersion type as theprojection exposure apparatus applying the step and repeat method.Accordingly, there is a risk that a tip portion of the projectionoptical system contacting the liquid may be corroded by the liquid,thereby leading to a failure to obtain a desired optical performance.

Meanwhile, an exposure process is performed while moving a wafer whenconfiguring the projection exposure apparatus of the liquid immersiontype as the projection exposure apparatus applying the step-and-scanmethod. Accordingly, it is necessary to fill the space between theprojection optical system and the wafer with the liquid in the course ofmoving the wafer. Since the projection optical system contacts theliquid, there is a risk that the tip portion of the projection opticalsystem contacting the liquid may be corroded by the liquid, therebyleading to a failure to obtain a desired optical performance.

An object of this invention is to provide an optical element configuredto avoid a tip portion of a projection optical system from beingcorroded by a liquid when applying the liquid immersion method, and toprovide an exposure apparatus including the optical element.

To attain the object the present invention provides the followingoptical elements and exposure apparatuses applying any of the opticalelements.

A first aspect of the present invention provides an optical element tobe used for an exposure apparatus, which is configured to illuminate amask with an exposure light beam for transferring a pattern on the maskonto a substrate through a projection optical system and to interpose agiven liquid in a space between a surface of the substrate and theprojection optical system. Here, the optical element includes a firstanti-dissolution member provided on a surface of a transmissive opticalelement on the substrate's side of the projection optical system.

According to the optical element of the first aspect, the firstanti-dissolution member is formed on the surface (a tip surface) of theoptical element. Therefore, it is possible to prevent dissolution of theoptical element and thereby to maintain an optical performance of theprojection optical system.

A second aspect of the present invention provides the optical elementaccording to the first aspect, in which the first anti-dissolutionmember includes a single-layer film having a protective function toprotect the optical element against the liquid.

A third aspect of the present invention provides the optical elementaccording to the second aspect, in which the single-layer film hassolubility in pure water equal to or below 1.0×10⁻⁷ grams per hundredgrams of water.

According to the optical elements of the second and third aspects, it ispossible to reduce an interface in comparison with a multilayer film.Therefore, it is possible to minimize an adverse effect of a chemicalreaction which is apt to occur when the liquid infiltrates into aninterface of a protective layer serving as an anti-dissolution film.Moreover, it is easier to form the film as compared to formation of theanti-dissolution film including the multilayer film.

A fourth aspect of the present invention provides the optical elementaccording to the first aspect, in which the first anti-dissolutionmember includes a multilayer film having a protective function toprotect the optical element against the liquid and an anti-reflectionfunction to prevent reflection of the exposure light beam.

A fifth aspect of the present invention provides the optical elementaccording to the fourth aspect, in which the multilayer film at leastincludes a layer having solubility in pure water equal to or below1.0×10⁻⁷ grams per hundred grams of water as the outermost layer, andmean reflectance of the multilayer film is equal to or below 2% when anexit angle of the exposure light beam is set to 50 degrees.

A sixth aspect of the present invention provides the optical elementaccording to the fourth aspect, in which the multilayer film includes nlayers (n is an integer), and when the layers are defined sequentiallyas a first layer, a second layer, and so forth to an n-th layer beingthe outermost layer, an odd-numbered layer has a higher refractive indexthan a refractive index of any of the adjacent optical element and anadjacent even-numbered layer. Moreover, the first to the n-th layershave the anti-reflection function as a whole.

A seventh aspect of the present invention provides the optical elementaccording to the fourth aspect, in which the multilayer film includes nlayers (n is an integer), and when the layers are defined sequentiallyas a first layer, a second layer, and so forth to an n-th layer beingthe outermost layer, an odd-numbered layer has a lower refractive indexthan a refractive index of any of the adjacent optical element and anadjacent even-numbered layer. Moreover, the first to the n-th layershave the anti-reflection function as a whole.

According to the optical element of any one of the fourth to seventhaspects, the multilayer film is formed on the surface of the opticalelement, and the multilayer film has the protective function to protectthe optical element against the liquid and the anti-reflection functionto prevent reflection of the exposure light beam (incident light from anexposure light source). Therefore, it is possible to provide the stableoptical element without being corroded by the liquid. Hence it ispossible to provide the optical element which can realize ahigh-performance projection exposure apparatus having high resolutionand a large depth of focus by use of the liquid immersion method.

An eighth aspect of the present invention provides the optical elementaccording to the first aspect, in which the first anti-dissolutionmember is made of at least one selected from the group consisting ofMgF₂, LaF₃, SrF₂, YF₃, LuF₃, HfF₄, NdF₃, GdF₃, YbF₃, DyF₃, AlF₃,Na₃AlF₆, 5NaF.3AlF₃, Al₂O₃, SiO₂, TiO₂, MgO, HfO₂, Cr₂O₃, ZrO₂, Ta₂O₅,and Nb₂O₅.

According to the optical element of the eighth aspect, it is possible toselect the anti-dissolution member to be formed on the optical element.Therefore, it is possible to select the most appropriateanti-dissolution member based on the material of the optical element,the environment where the optical element is placed, the type of theliquid used for soaking the optical element, and the like.

A ninth aspect of the present invention provides the optical elementaccording to the fourth aspect, in which the multilayer film includes nlayers (n is an integer) and has a layer structure, which is expressedas first layer/second layer/other successive layers/n-th layer, of oneselected from the group consisting of (i) LaF₃/MgF₂, (ii) MgF₂/SiO₂,(iii) MgF₂/SiO₂/SiO₂, (iv) LaF₃/MgF₂/SiO₂, (v) LaF₃/MgF₂/Al₂O₃, (vi)LaF₃/MgF₂/Al₂O₃/SiO₂, (vii) LaF₃/MgF₂/LaF₃/MgF₂, (viii)LaF₃/MgF₂/LaF₃/SiO₂, (ix) LaF₃/MgF₂/LaF₃/MgF₂/SiO₂, and (x)LaF₃/MgF₂/LaF₃/Al₂O₃/SiO₂.

According to the optical element of the ninth aspect, the multilayerfilm has the protective function for a given time period, and istherefore capable of protecting the optical element against water as theimmersion liquid for ten years, for example. Hence it is possible toprovide the optical element which can realize a high-performanceprojection exposure apparatus having high resolution and a large depthof focus by use of the liquid immersion method. At the same time, it ispossible to provide the stable optical element without causing corrosionby the liquid for the given time period.

A tenth aspect of the present invention provides the optical elementaccording to the first aspect, in which the first anti-dissolutionmember is formed by at least one film forming method selected from thegroup consisting of a vacuum vapor deposition method, an ion beamassisted vapor deposition method, a gas cluster ion beam assisted vapordeposition method, an ion plating method, an ion beam sputtering method,a magnetron sputtering method, a bias sputtering method, an electroncyclotron resonance (ECR) sputtering method, a radio frequency (RF)sputtering method, a thermal chemical vapor deposition (thermal CVD)method, a plasma enhanced CVD method, and a photo CVD method.

According to the optical element of the tenth aspect, it is possible toselect the film forming method when forming the anti-dissolution memberon the optical element. Therefore, it is possible to form theanti-dissolution member in the optimal condition on the optical elementby selecting the most appropriate film forming method for the materialof the anti-dissolution member.

An eleventh aspect of the present invention provides the optical elementaccording to the first aspect, in which the first anti-dissolutionmember includes a film made of an oxide formed by a wet film formingmethod.

According to the optical element of the eleventh aspect, the oxideanti-dissolution film for preventing dissolution to the liquid is formedon the surface of the transmissive optical element on the substrate'sside of the projection optical system by use of the wet film formingmethod characterized by high homogeneity and a high filling performancerelative to voids. Therefore, it is possible to prevent infiltration toand corrosion of the transmissive optical element by the given liquidinterposed between the surface of the substrate and the projectionoptical system, and thereby to maintain the optical performance of theprojection optical system. As a result, when this transmissive opticalelement is applied to the exposure apparatus of the liquid immersiontype, it is possible to avoid dissolution of the transmissive opticalelement in the liquid and thereby to maintain the performance of theexposure apparatus. In addition, it is not necessary to replace thetransmissive optical element frequently. Therefore, it is possible tomaintain high throughput of the exposure apparatus.

Here, when the transmissive optical element is made of calcium fluoridehaving a smoothly polished surface, it is preferable to subject thetransmissive optical element to a surface treatment for increasing thesurface area of the transmissive optical element by roughening thesurface of the transmissive optical element to the extent not to degradethe optical performance of the projection optical system in order toenhance adhesion between the transmissive optical element and the oxideanti-dissolution film.

A twelfth aspect of the present invention provides the optical elementaccording to the fourth aspect, in which the multilayer film includes afirst film formed by a dry film forming method and a second film made ofan oxide formed by a wet film forming method.

According to the optical element of the twelfth aspect, the first filmis formed on the surface of the transmissive optical element on thesubstrate's side of the projection optical system by use of the dry filmforming method, and the oxide film serving as the second film is formedon a surface of the first film thus formed by use of the wet filmforming method. Therefore, even when the transmissive optical element ismade of calcium fluoride having a smoothly polished surface, it ispossible to attach the first film firmly to the transmissive opticalelement as the first film is formed by the dry film forming method.Meanwhile, it is possible to allow the first film to function as anadhesion reinforcing film to achieve firm attachment of the transmissiveoptical element to the second film.

Moreover, the second film is formed by use of the wet film formingmethod characterized by high homogeneity and a high filling performancerelative to voids. Accordingly, voids on the first film are eliminatedby penetration of the second film. Therefore, it is possible to preventinfiltration to and corrosion of the transmissive optical element by thegiven liquid interposed between the surface of the substrate and theprojection optical system, and thereby to maintain the opticalperformance of the projection optical system. As a result, when thistransmissive optical element is applied to the exposure apparatus of theliquid immersion type, it is possible to avoid dissolution of thetransmissive optical element in the liquid because the first film andthe second film are not detached from the transmissive optical element.In this way, it is possible to maintain the performance of the exposureapparatus. In addition, it is not necessary to replace the transmissiveoptical element frequently. Therefore, it is possible to maintain highthroughput of the exposure apparatus.

A thirteenth aspect of the present invention provides the opticalelement according to the fourth aspect, in which the multilayer film atleast includes a SiO₂ film formed by a wet film forming method as theoutermost layer.

According to the optical element of the thirteenth aspect, the film onthe outermost layer has the protective function for a given time period,and is therefore capable of protecting the optical element against wateras the immersion liquid for ten years, for example. Hence it is possibleto provide the optical element which can realize a high-performanceprojection exposure apparatus having high resolution and a large depthof focus by use of the liquid immersion method. At the same time, it ispossible to provide the stable optical element without being corroded bythe liquid for the given time period.

A fourteenth aspect of the present invention provides the opticalelement according to the thirteenth aspect, which further includes aSiO₂ film formed by a dry film forming method to be provided on theoptical element's side of the SiO₂ film formed by the wet film formingmethod.

According to the optical element of the fourteenth aspect, bonding powerbetween the silicon dioxide film formed by the dry film forming methodand the silicon dioxide film formed by the wet film forming method isstrengthened, and it is thereby possible to attach the both films morefirmly. As a result, when this transmissive optical element is appliedto the exposure apparatus of the liquid immersion type, it is possibleto avoid separation of the both films and to avoid dissolution of thetransmissive optical element in the liquid. In this way, it is possibleto maintain the performance of the exposure apparatus. In addition, itis not necessary to replace the transmissive optical element frequently.Therefore, it is possible to maintain high throughput of the exposureapparatus.

A fifteenth aspect of the present invention provides the optical elementaccording to the first aspect, in which the first anti-dissolutionmember includes a thin plate having a protective function to protect theoptical element against the liquid and an anti-reflection function toprevent reflection of the exposure light beam. Here, the thin plate isdetachably joined to a surface of the optical element.

A sixteenth aspect of the present invention provides the optical elementaccording to the fifteenth aspect, in which the thin plate is joined tothe surface of the optical element by optical contact, and meanreflectance of the thin plate is equal to or below 2% when an exit angleof the exposure light beam is set to 50 degrees.

A seventeenth aspect of the present invention provides the opticalelement according to the fifteenth aspect, in which the thin plate ismade of at least one selected from the group consisting of a fluoride,an oxide, and a resin.

An eighteenth aspect of the present invention provides the opticalelement according to the fifteenth aspect, in which the thin plate is atleast one selected from the group consisting of a fused silica thinplate, a magnesium fluoride thin plate, a calcium fluoride thin plate,and a polytetrafluoroethylene thin plate.

According to the optical element of any one of the fifteenth toeighteenth aspects, the thin plate having the protective function toprotect the surface of the optical element against the liquid and thefunction to prevent reflection of the exposure light beam is joined tothe surface of the optical element, and this optical member used thereinis detachable without damaging the surface condition of the opticalelement. Therefore, it is possible to provide the stable optical memberwithout being corroded by the liquid. Hence it is possible to providethe optical member which can realize a high-performance projectionexposure apparatus having high resolution and a large depth of focus byuse of the liquid immersion method. Moreover, when the thin plate isjoined to the optical element by the optical contact, it is possible tofurther enhance the protective function against the liquid.

A nineteenth aspect of the present invention provides the opticalelement according to the first aspect, which further includes a secondanti-dissolution member on a side surface of the transmissive opticalelement on the substrate's side of the projection optical system.

According to the optical element of the nineteenth aspect, the secondanti-dissolution member is formed on the surface (a tip surface) on thesubstrate's side of the optical element and on the side surface (atapered surface) of the optical element, or in other words, at portionswhere the exposure light beam does not pass through. Therefore, it ispossible to prevent dissolution of the optical element from the surfaceon the substrate's side and to prevent dissolution of the opticalelement from the side surface as well. In this way, it is possible tomaintain the optical performance of the projection optical system.

A twentieth aspect of the present invention provides the optical elementaccording to the nineteenth aspect, in which each of the firstanti-dissolution member and the second anti-dissolution member includesa film that is formed by use of an identical material.

According to the optical element of the twentieth aspect, it is possibleto form the anti-dissolution films on the surface on the substrate'sside of the optical element and on the side surface of the opticalelement at the same time. Therefore, it is possible to form theanti-dissolution films by a simple process.

A twenty-first aspect of the present invention provides the opticalelement according to the twentieth aspect, in which the film formed byuse of the identical material is formed by a wet film forming method.

According to the optical element of the twenty-first aspect, it ispossible to form the anti-dissolution films on the surface on thesubstrate's side of the optical element and on the side surface of theoptical element at the same time. Therefore, it is possible to protectthe substrate without generating any gaps.

A twenty-second aspect of the present invention provides the opticalelement according to the twentieth aspect, in which the identicalmaterial is any of MgF₂ and SiO₂.

According to the optical element of the twenty-second aspect, it ispossible to protect the substrate because the identical material iseither MgF₂ or the SiO₂.

A twenty-third aspect of the present invention provides the opticalelement according to the nineteenth aspect, in which the firstanti-dissolution member includes a hydrophilic anti-dissolution film,and the second anti-dissolution member includes a hydrophobicanti-dissolution film.

Here, the anti-dissolution film formed on the side surface of theoptical element is the anti-dissolution film having an excellenthydrophobic performance as compared to the anti-dissolution film formedon the surface on the substrate's side of the optical element, while theanti-dissolution film formed on the surface on the substrate's side ofthe optical element is the anti-dissolution film having an excellenthydrophilic performance as compared to the anti-dissolution film formedon the side surface of the optical element.

According to the optical element of the twenty-third aspect, it ispossible to guide the liquid attached to the side surface of the opticalelement easily to the substrate's side because the anti-dissolution filmformed on the side surface of the optical element is the hydrophobicanti-dissolution film. Moreover, it is possible to fill the spacebetween the surface on the substrate's side of the optical element andthe substrate constantly with the liquid because the anti-dissolutionfilm formed on the surface on the substrate's side of the opticalelement is the hydrophilic anti-dissolution film.

A twenty-fourth aspect of the present invention provides the opticalelement according to the nineteenth aspect, in which the secondanti-dissolution member includes a metal anti-dissolution film having aprotective function to protect the optical element against the liquid.

According to the optical element of the twenty-fourth aspect, the sidesurface (the tapered surface) of the transmissive optical element on thesubstrate's side of the projection optical system is provided with themetal anti-dissolution film, which is insoluble to the given liquidinterposed between the surface of the substrate and the projectionoptical system. Therefore, it is possible to prevent infiltration to andcorrosion of the transmissive optical element by the liquid and therebyto maintain the optical performance of the projection optical system. Asa result, when this transmissive optical element is applied to theexposure apparatus of the liquid immersion type, it is possible tomaintain the performance of the exposure apparatus because thetransmissive optical element does not dissolve in the liquid. Inaddition, it is not necessary to replace the transmissive opticalelement frequently. Therefore, it is possible to maintain highthroughput of the exposure apparatus.

A twenty-fifth aspect of the present invention provides the opticalelement according to the twenty-fourth aspect, in which the secondanti-dissolution member further includes an adhesion reinforcing filmformed between the side surface of the optical element and the metalanti-dissolution film.

According to the optical element of the twenty-fifth aspect, the metalanti-dissolution film is formed on the surface of the adhesionreinforcing film formed on the side surface of the transmissive opticalelement on the substrate's side of the projection optical system, and itis possible to attach the metal anti-dissolution film closely to thetransmissive optical element. Therefore, it is possible to preventinfiltration to and corrosion of the transmissive optical element by thegiven liquid interposed between the surface of the substrate and theprojection optical system, and thereby to maintain the opticalperformance of the projection optical system. Moreover, when thistransmissive optical element is applied to the exposure apparatus of theliquid immersion type, it is possible to maintain the performance of theexposure apparatus because the metal anti-dissolution film is notdetached from the transmissive optical element and the transmissiveoptical element does not dissolve in the liquid. In addition, it is notnecessary to replace the transmissive optical element frequently.Therefore, it is possible to maintain high throughput of the exposureapparatus.

A twenty-sixth aspect of the present invention provides the opticalelement according to the twenty-fourth aspect, in which the secondanti-dissolution member further includes a protective film for the metalanti-dissolution film. Here, the protective film is formed on a surfaceof the metal anti-dissolution film.

According to the optical element of the twenty-sixth aspect, theprotective film for the metal anti-dissolution film is formed on thesurface of the metal anti-dissolution film formed on the side surface ofthe transmissive optical element on the substrate's side of theprojection optical system, and it is possible to prevent damage on thesoft metal anti-dissolution film having low abrasion resistance andthereby to protect the metal anti-dissolution film. Therefore, it ispossible to prevent infiltration to and corrosion of the transmissiveoptical element by the given liquid interposed between the surface ofthe substrate and the projection optical system, and thereby to maintainthe optical performance of the projection optical system. Moreover, whenthis transmissive optical element is applied to the exposure apparatusof the liquid immersion type, it is possible to maintain the performanceof the exposure apparatus because the transmissive optical element doesnot dissolve in the liquid. In addition, it is not necessary to replacethe transmissive optical element frequently. Therefore, it is possibleto maintain high throughput of the exposure apparatus.

A twenty-seventh aspect of the present invention provides the opticalelement according to the twenty-fourth aspect, in which the metalanti-dissolution film has solubility in water equal to or below 2 pptand packing density equal to or above 95%.

According to the optical element of the twenty-seventh aspect, theanti-dissolution film having the solubility in water equal to or below 2ppt is formed on the side surface of the transmissive optical element onthe substrate's side of the projection optical system, and it ispossible to maintain the optical performance of the projection opticalsystem without causing dissolution of the transmissive optical elementto the given liquid interposed between the surface of the substrate andthe projection optical system. Moreover, since the anti-dissolution filmhaving the packing density equal to or above 95% is formed on the sidesurface of the transmissive optical element on the substrate's side ofthe projection optical system, it is possible to prevent infiltration toand corrosion of the transmissive optical element by the liquid, andthereby to maintain the optical performance of the projection opticalsystem. Therefore, when this transmissive optical element is applied tothe exposure apparatus of the liquid immersion type, it is possible tomaintain the performance of the exposure apparatus because thetransmissive optical element does not dissolve in the liquid. Inaddition, it is not necessary to replace the transmissive opticalelement frequently. Therefore, it is possible to maintain highthroughput of the exposure apparatus.

A twenty-eighth aspect of the present invention provides the opticalelement according to the twenty-fourth aspect, in which the metalanti-dissolution film is made of at least one selected from the groupconsisting of Au, Pt, Ag, Ni, Ta, W, Pd, Mo, Ti, and Cr.

According to the optical element of the twenty-eighth aspect, the metalanti-dissolution film constructed as the film made of at least one ofAu, Pt, Ag, Ni, Ta, W, Pd, Mo, Ti, and Cr is formed on the side surface(the tapered surface) of the transmissive optical element on thesubstrate's side of the projection optical system, or in other words, ata portion where the exposure light beam does not pass through.Therefore, even when this transmissive optical element is applied to theexposure apparatus of the liquid immersion type, it is possible tocontinue exposure in the optimal condition without shielding theexposure light beam by the metal anti-dissolution film.

A twenty-ninth aspect of the present invention provides the opticalelement according to the twenty-fifth aspect, in which the adhesionreinforcing film is made of at least one selected from the groupconsisting of Ta and Cr.

According to the optical element of the twenty-ninth aspect, theadhesion reinforcing film constructed as the film made of at least oneof Ta and Cr is formed between the transmissive optical element and theanti-dissolution film. Therefore, it is possible to improve adhesionbetween the side surface of the transmissive optical element and theanti-dissolution film. As a result, when this transmissive opticalelement is applied to the exposure apparatus of the liquid immersiontype, it is possible to avoid detachment of the anti-dissolution filmfrom the transmissive optical element and to avoid dissolution of thetransmissive optical element in the liquid. In this way, it is possibleto maintain the performance of the exposure apparatus. In addition, itis not necessary to replace the transmissive optical element frequently.Therefore, it is possible to maintain high throughput of the exposureapparatus.

A thirtieth aspect of the present invention provides the optical elementaccording to the twenty-sixth aspect, in which the protective film forthe metal anti-dissolution film is made of at least one selected fromthe group consisting of SiO₂, Y₂O₃, Nd₂F₃, Cr₂O₃, Ta₂O₅, Nb₂O₅, TiO₂,ZrO₂, HfO₂, and La₂O₃.

According to the optical element of the thirtieth aspect, it is possibleto select the protective film for the metal anti-dissolution film to beformed on the surface of the metal anti-dissolution film that is formedon the transmissive optical element. Therefore, it is possible to selectthe most appropriate protective film for the metal anti-dissolution filmbased on the material of the transmissive optical element, theenvironment where the transmissive optical element is placed, the typeof the given liquid to be interposed between the surface of thesubstrate and the projection optical system, and the like.

A thirty-first aspect of the present invention provides the opticalelement according to the nineteenth aspect, in which the secondanti-dissolution member includes a light-shielding film.

A thirty-second aspect of the present invention provides the opticalelement according to the thirty-first aspect, in which thelight-shielding film is formed of any of a metal film and a metal oxidefilm.

A thirty-third aspect of the present invention provides the opticalelement according to the thirty-second aspect, in which the metal filmis made of at least one selected from the group consisting of Au, Pt,Ag, Ni, Ta, W, Pd, Mo, Ti, and Cr, and the metal oxide film is made ofat least one selected from the group consisting of ZrO₂, HfO₂, TiO₂,Ta₂O₅, SiO, and Cr₂O₃.

According to the optical element of any one of the thirty-first tothirty-third aspects, it is possible to prevent irradiation of theexposure light beam and reflected light of the exposure light beam froma wafer onto a sealing member formed in a peripheral portion of the sidesurface (the tapered surface) of the transmissive optical element on thesubstrate's side of the projection optical system by use of thelight-shielding film. In this way, it is possible to preventdeterioration of the sealing member.

A thirty-fourth aspect of the present invention provides the opticalelement according to the first aspect, which further includes an opticalmember joined to a surface of the optical element by optical contactthrough the first anti-dissolution member.

According to the optical element of the thirty-fourth aspect, theoptical member optically contacts the optical element through the firstanti-dissolution member. Therefore, it is possible to attach the opticalmember firmly even to the optical element applying a fluoride materialas the base material due to the presence of the appropriateanti-dissolution member. As a result, it is possible to protect theoptical element by use of the optical member, and thereby to maintain aperformance of an optical system incorporating the optical element overa long period of time.

A thirty-fifth aspect of the present invention provides the opticalelement according to the thirty-fourth aspect, in which the firstanti-dissolution member is a film made of SiO₂, and the optical memberis a member made of silica glass.

According to the optical element of the thirty-fifth aspect, a surfaceof the first anti-dissolution member used for the optical contact ismade of silicon dioxide. Therefore, it is possible to enhance bondingstrength to the optical member by use of a hydroxyl group in the silicondioxide surface. Meanwhile, it is possible to form the silicon dioxidefilm at high controllability and thereby to achieve high film quality.Moreover, the optical member made of silica glass can achieveparticularly excellent water resistance and bonding strength, andfavorable transmission of ultraviolet light and the like.

A thirty-sixth aspect of the present invention provides the opticalelement according to the first aspect, in which the exposure light beamis an ArF laser beam, the optical element is an element made of calciumfluoride, and crystal orientation of the surface of the optical elementis defined as a (111) plane.

According to the optical element of the thirty-sixth aspect, the opticalelement is applied to the exposure apparatus configured to emit the ArFlaser beam as the exposure light beam. Therefore, it is possible toachieve a high resolution performance. Moreover, the optical element ismade of calcium fluoride and is therefore applicable to a laser having ashort wavelength such as the ArF laser. Meanwhile, when the opticalelement is made of calcium fluoride, the optical element can achieve afavorable transmission performance of ultraviolet light and finedurability against the ultraviolet light and the like. In addition, theanti-dissolution film to be formed thereon, or lanthanum fluoride inparticular, is subjected to heteroepitaxial growth when the film isformed on a film forming surface of calcium fluoride having the crystalorientation of the (111) plane. Therefore, the anti-dissolution filmformed thereon becomes extremely dense and achieves a crystallinestructure with very few defects.

A thirty-seventh aspect of the present invention provides an opticalelement to be used for an exposure apparatus, which is configured toilluminate a mask with an exposure light beam for transferring a patternon the mask onto a substrate through a projection optical system and tointerpose a given liquid in a space between a surface of the substrateand the projection optical system. Here, the optical element includes alight-shielding film provided on a side surface of a transmissiveoptical element on the substrate's side of the projection opticalsystem.

A thirty-eighth aspect of the present invention provides the opticalelement according to the thirty-seventh aspect, in which thelight-shielding film is formed of any of a metal film and a metal oxidefilm.

A thirty-ninth aspect of the present invention provides the opticalelement according to the thirty-eighth aspect, in which the metal filmis made of at least one selected from the group consisting of Au, Pt,Ag, Ni, Ta, W, Pd, Mo, Ti, and Cr, and the metal oxide film is made ofat least one selected from the group consisting of ZrO₂, HfO₂, TiO₂,Ta₂O₅, SiO, and Cr₂O₃.

According to the optical element of any one of the thirty-seventh tothirty-ninth aspects, it is possible to prevent irradiation of theexposure light beam and reflected light of the exposure light beam froma wafer onto the sealing member formed in the peripheral portion of theside surface (the tapered surface) of the transmissive optical elementon the substrate's side of the projection optical system by use of thelight-shielding film. In this way, it is possible to preventdeterioration of the sealing member.

A fortieth aspect of the present invention provides an exposureapparatus configured to illuminate a mask with an exposure light beamfor transferring a pattern on the mask onto a substrate through aprojection optical system and to interpose a given liquid in a spacebetween a surface of the substrate and the projection optical system.Here, the exposure apparatus includes a first anti-dissolution memberprovided on a surface of a transmissive optical element on thesubstrate's side of the projection optical system.

According to the exposure apparatus of the fortieth aspect, the firstanti-dissolution member is formed on the surface (a tip surface) of theoptical element. Therefore, the optical element does not dissolve in theliquid filling the space between the tip portion of the projectionoptical system and the substrate. Accordingly, it is possible to avoidfrequent replacement of the optical element, and thereby to maintainhigh throughput of the exposure apparatus. In addition, since theoptical element does not dissolve in the liquid, it is possible tomaintain an optical performance of the projection optical system and tocontinue exposure in the optimal condition.

A forty-first aspect of the present invention provides the exposureapparatus according to the fortieth aspect, in which the firstanti-dissolution member includes a single-layer film having a protectivefunction to protect the optical element against the liquid.

According to the exposure apparatus of the forty-first aspect, it ispossible to reduce an interface in comparison with a multilayer film.Therefore, it is possible to minimize an adverse effect of a chemicalreaction which is apt to occur when the liquid infiltrates into aninterface of a protective layer serving as an anti-dissolution film.Moreover, it is easier to form the film as compared to formation of theanti-dissolution film including the multilayer film.

A forty-second aspect of the present invention provides the exposureapparatus according to the fortieth aspect, in which the firstanti-dissolution member includes a multilayer film having a protectivefunction to protect the optical element against the liquid and ananti-reflection function to prevent reflection of the exposure lightbeam.

According to the exposure apparatus of the forty-second aspect, the tipof the optical element is not corroded by the liquid. Therefore, it isnot necessary to stop operation of the apparatus in order to replace thecorroded optical element, and it is thereby possible to manufacture endproducts efficiently. Moreover, since the optical element of the presentinvention has corrosion resistance and a stable optical characteristic,it is possible to stabilize the quality of end products to bemanufactured by use of the exposure apparatus embedding the opticalelement of the present invention.

A forty-third aspect of the present invention provides the exposureapparatus according to the fortieth aspect, in which the firstanti-dissolution member is made of at least one selected from the groupconsisting of MgF₂, LaF₃, SrF₂, YF₃, LuF₃, HfF₄, NdF₃, GdF₃, YbF₃, DyF₃,AlF₃, Na₃AlF₆, 5NaF.3AlF₃, Al₂O₃, SiO₂, TiO₂, MgO, HfO₂, Cr₂O₃, ZrO₂,Ta₂O₅, and Nb₂O₅.

According to the exposure apparatus of the forty-third aspect, it ispossible to select the anti-dissolution member to be formed on theoptical element. Therefore, it is possible to select the mostappropriate anti-dissolution member based on the material of the opticalelement, the environment where the optical element is placed, the typeof the liquid used for filling the space between the projection opticalsystem and the substrate, and the like.

A forty-fourth aspect of the present invention provides the exposureapparatus according to the forty-second aspect, in which the multilayerfilm includes n layers (n is an integer) and has a layer structure,which is expressed as first layer/second layer/other successivelayers/n-th layer, of one selected from the group consisting of (i)LaF₃/MgF₂, (ii) MgF₂/SiO₂, (iii) MgF₂/SiO₂/SiO₂, (iv) LaF₃/MgF₂/SiO₂,(v) LaF₃/MgF₂/Al₂O₃, (vi) LaF₃/MgF₂/Al₂O₃/SiO₂, (vii)LaF₃/MgF₂/LaF₃/MgF₂, (viii) LaF₃/MgF₂/LaF₃/SiO₂, (ix)LaF₃/MgF₂/LaF₃/MgF₂/SiO₂, and (x) LaF₃/MgF₂/LaF₃/Al₂O₃/SiO₂.

According to the exposure apparatus of the forty-fourth aspect, themultilayer film has the protective function for a given time period, andis therefore capable of protecting the optical element against water asthe immersion liquid for ten years, for example. Hence it is possible toprovide the high-performance exposure apparatus having high resolutionand a large depth of focus by use of the liquid immersion method. At thesame time, it is possible to provide the stable exposure apparatushaving the stable optical characteristic without being corroded by theliquid for the given time period.

A forty-fifth aspect of the present invention provides the exposureapparatus according to the fortieth aspect, in which the firstanti-dissolution member includes a film made of an oxide formed by a wetfilm forming method.

According to the exposure apparatus of the forty-fifth aspect, theanti-dissolution oxide film for preventing dissolution to the liquid isformed on the surface of the transmissive optical element on thesubstrate's side of the projection optical system by use of the wet filmforming method characterized by high homogeneity and a high fillingperformance relative to voids. Therefore, it is possible to preventinfiltration to and corrosion of the transmissive optical element by thegiven liquid interposed between the surface of the substrate and theprojection optical system, and thereby to maintain the opticalperformance of the projection optical system. As a result, it ispossible to avoid dissolution of the transmissive optical element in theliquid and thereby to maintain the performance of the exposureapparatus. In addition, it is not necessary to replace the transmissiveoptical element frequently. Therefore, it is possible to maintain highthroughput of the exposure apparatus.

Here, when the transmissive optical element is made of calcium fluoridehaving a smoothly polished surface, it is preferable to subject thetransmissive optical element to a surface treatment for increasing thesurface area of the transmissive optical element by roughening thesurface of the transmissive optical element to the extent not to degradethe optical performance of the projection optical system in order toenhance adhesion between the transmissive optical element and theanti-dissolution oxide film.

A forty-sixth aspect of the present invention provides the exposureapparatus according to the forty-second aspect, in which the multilayerfilm includes a first film formed by a dry film forming method and asecond film made of an oxide formed by a wet film forming method.

According to the exposure apparatus of the forty-sixth aspect, the firstfilm and the second film formed on the transmissive optical element onthe substrate's side of the projection optical system are not detachedfrom the transmissive optical element. Moreover, the transmissiveoptical element does not dissolve in the liquid filling the spacebetween the tip portion of the projection optical system and thesubstrate. Hence it is possible to maintain the optical performance ofthe projection optical system and to continue exposure in the optimalcondition. In addition, it is not necessary to replace the transmissiveoptical element frequently. Therefore, it is possible to maintain highthroughput of the exposure apparatus.

A forty-seventh aspect of the present invention provides the exposureapparatus according to the fortieth aspect, in which the firstanti-dissolution member includes a thin plate having a protectivefunction to protect the optical element against the liquid and ananti-reflection function to prevent reflection of the exposure lightbeam. Here, the thin plate is detachably joined to a surface of theoptical element.

According to the exposure apparatus of the forty-seventh aspect, the tipof the optical element is not corroded by the liquid. Therefore, it isnot necessary to stop operation of the exposure apparatus in order toreplace the corroded optical element, and it is thereby possible tomanufacture end products efficiently. Moreover, since the opticalelement of the present invention has the corrosion resistance and thestable optical characteristic, it is possible to stabilize the qualityof end products to be manufactured by use of the exposure apparatusembedding the optical element of the present invention.

A forty-eighth aspect of the present invention provides the exposureapparatus according to the fortieth aspect, which further includes asecond anti-dissolution member on a side surface of the transmissiveoptical element on the substrate's side of the projection opticalsystem.

According to the exposure apparatus of the forty-eighth aspect, thesecond anti-dissolution member is formed on the surface (a tip surface)on the substrate's side of the optical element and on the side surface(a tapered surface) of the optical element, or in other words, atportions where the exposure light beam does not pass through. Therefore,it is possible to prevent dissolution of the optical element in theliquid filling the space between the tip portion of the projectionoptical system and the substrate. Hence it is not necessary to replacethe optical element frequently, and it is possible to maintain highthroughput of the exposure apparatus. In addition, since the opticalelement does not dissolve in the liquid, it is possible to maintain theoptical performance of the projection optical system and to continueexposure in the optimal condition.

A forty-ninth aspect of the present invention provides the exposureapparatus according to the forty-eighth aspect, in which each of thefirst anti-dissolution member and the second anti-dissolution memberincludes a film that is formed by use of an identical material.

According to the exposure apparatus of the forty-ninth aspect, it ispossible to form the anti-dissolution films on the surface on thesubstrate's side of the optical element and on the side surface of theoptical element at the same time. Therefore, it is possible to form theanti-dissolution films by a simple process.

A fiftieth aspect of the present invention provides the exposureapparatus according to the forty-eighth aspect, in which the secondanti-dissolution member includes a metal anti-dissolution film having aprotective function to protect the optical element against the liquid.

According to the exposure apparatus of the fiftieth aspect, the sidesurface of the transmissive optical element on the substrate's side ofthe projection optical system is provided with the metalanti-dissolution film, which is insoluble to the given liquid interposedbetween the surface of the substrate and the projection optical system.Therefore, it is possible to prevent infiltration to and corrosion ofthe transmissive optical element by the liquid and thereby to maintainthe optical performance of the projection optical system. As a result,it is possible to avoid dissolution of the transmissive optical elementin the liquid and thereby to maintain the performance of the exposureapparatus. In addition, it is not necessary to replace the transmissiveoptical element frequently. Therefore, it is possible to maintain highthroughput of the exposure apparatus.

A fifty-first aspect of the present invention provides the exposureapparatus according to the fiftieth aspect, in which the secondanti-dissolution member further includes an adhesion reinforcing filmformed between the side surface of the optical element and the metalanti-dissolution film.

According to the exposure apparatus of the fifty-first aspect, the metalanti-dissolution film is formed on the surface of the adhesionreinforcing film formed on the side surface of the transmissive opticalelement on the substrate's side of the projection optical system, and itis possible to attach the metal anti-dissolution film closely to thetransmissive optical element. Therefore, it is possible to preventinfiltration to and corrosion of the transmissive optical element by thegiven liquid interposed between the surface of the substrate and theprojection optical system, and thereby to maintain the opticalperformance of the projection optical system. Moreover, it is possibleto maintain the performance of the exposure apparatus because the metalanti-dissolution film is not detached from the transmissive opticalelement and the transmissive optical element does not dissolve in theliquid. In addition, it is not necessary to replace the transmissiveoptical element frequently. Therefore, it is possible to maintain highthroughput of the exposure apparatus.

A fifty-second aspect of the present invention provides the exposureapparatus according to the fiftieth aspect, in which the secondanti-dissolution member further includes a protective film for the metalanti-dissolution film. Here, the protective film is formed on a surfaceof the metal anti-dissolution film.

According to the exposure apparatus of the fifty-second aspect, theprotective film for the metal anti-dissolution film is formed on thesurface of the metal anti-dissolution film formed on the side surface ofthe transmissive optical element on the substrate's side of theprojection optical system, and it is possible to prevent damage on thesoft metal anti-dissolution film having low abrasion resistance andthereby to protect the metal anti-dissolution film. Therefore, it ispossible to prevent infiltration to and corrosion of the transmissiveoptical element by the given liquid interposed between the surface ofthe substrate and the projection optical system, and thereby to maintainthe optical performance of the projection optical system. Moreover, itis possible to maintain the performance of the exposure apparatusbecause the transmissive optical element does not dissolve in theliquid. In addition, it is not necessary to replace the transmissiveoptical element frequently. Therefore, it is possible to maintain highthroughput of the exposure apparatus.

A fifty-third aspect of the present invention provides the exposureapparatus according to the fiftieth aspect, in which the metalanti-dissolution film is made of at least one selected from the groupconsisting of Au, Pt, Ag, Ni, Ta, W, Pd, Mo, Ti, and Cr.

According to the exposure apparatus of the fifty-third aspect, the metalanti-dissolution film constructed as the film made of at least one ofAu, Pt, Ag, Ni, Ta, W, Pd, Mo, Ti, and Cr is formed on the side surface(the tapered surface) of the transmissive optical element on thesubstrate's side of the projection optical system, or in other words, ata portion where the exposure light beam does not pass through.Therefore, it is possible to continue exposure in the optimal conditionwithout shielding the exposure light beam by the metal anti-dissolutionfilm.

A fifty-fourth aspect of the present invention provides the exposureapparatus according to the fifty-second aspect, in which the protectivefilm for the metal anti-dissolution film is made of at least oneselected from the group consisting of SiO₂, Y₂O₃, Nd₂F₃, Cr₂O₃, Ta₂O₅,Nb₂O₅, TiO₂, ZrO₂, HfO₂, and La₂O₃.

According to the exposure apparatus of the fifty-fourth aspect, it ispossible to select the protective film for the metal anti-dissolutionfilm to be formed on the surface of the metal anti-dissolution film thatis formed on the transmissive optical element. Therefore, it is possibleto select the most appropriate protective film for the metalanti-dissolution film based on the material of the transmissive opticalelement, the environment where the transmissive optical element isplaced, the type of the given liquid to be interposed between thesurface of the substrate and the projection optical system, and thelike.

A fifty-fifth aspect of the present invention provides the exposureapparatus according to the forty-eighth aspect, in which the secondanti-dissolution member includes a light-shielding film.

A fifty-sixth aspect of the present invention provides the exposureapparatus according to the fifty-fifth aspect, in which thelight-shielding film is formed of any of a metal film and a metal oxidefilm.

A fifty-seventh aspect of the present invention provides the exposureapparatus according to the fifty-sixth aspect, in which the metal filmis made of at least one selected from the group consisting of Au, Pt,Ag, Ni, Ta, W, Pd, Mo, Ti, and Cr, and the metal oxide film is made ofat least one selected from the group consisting of ZrO₂, HfO₂, TiO₂,Ta₂O₅, SiO, and Cr₂O₃.

According to the exposure apparatus of any one of the fifty-fifth tofifty-seventh aspects, it is possible to prevent irradiation of theexposure light beam and reflected light of the exposure light beam froma wafer onto a sealing member formed in a peripheral portion of the sidesurface (the tapered surface) of the transmissive optical element on thesubstrate's side of the projection optical system by use of thelight-shielding film. In this way, it is possible to preventdeterioration of the sealing member.

A fifty-eighth aspect of the present invention provides the exposureapparatus according to the fortieth aspect, which further includes anoptical member joined to a surface of the optical element by opticalcontact through the first anti-dissolution member.

According to the exposure apparatus of the fifty-eighth aspect, theexposure apparatus applies the projection optical system which embedsthe optical member achieving excellent optical contact. Therefore, it ispossible to perform an exposure process of the liquid immersion typewhile maintaining a high performance for over a long period of time.

A fifty-ninth aspect of the present invention provides the exposureapparatus according to the fortieth aspect, in which the exposure lightbeam is an ArF laser beam, the optical element is an element made ofcalcium fluoride, and crystal orientation of the surface of the opticalelement is defined as a (111) plane.

According to the exposure apparatus of the fifty-ninth aspect, theexposure apparatus configured to emit the ArF laser beam as the exposurelight beam can achieve a high resolution performance. Moreover, theoptical element is made of calcium fluoride and is therefore applicableto a laser having a short wavelength such as the ArF laser. Meanwhile,when the optical element is made of calcium fluoride, the opticalelement can achieve a favorable transmission performance of ultravioletlight and the like and fine durability against the ultraviolet light andthe like. In addition, the anti-dissolution film to be formed thereon,or lanthanum fluoride in particular, is subjected to heteroepitaxialgrowth when the film is formed on a film forming surface of calciumfluoride having the crystal orientation of the (111) plane. Therefore,the anti-dissolution film formed thereon becomes extremely dense andachieves a crystalline structure with very few defects.

A sixtieth aspect of the present invention provides an exposureapparatus configured to illuminate a mask with an exposure light beamfor transferring a pattern on the mask onto a substrate through aprojection optical system, and to interpose a given liquid in a spacebetween a surface of the substrate and the projection optical system.Here, the exposure apparatus includes a light-shielding film provided ona side surface of a transmissive optical element on the substrate's sideof the projection optical system.

A sixty-first aspect of the present invention provides the exposureapparatus according to the sixtieth aspect, in which the light-shieldingfilm is formed of any of a metal film and a metal oxide film.

A sixty-second aspect of the present invention provides the exposureapparatus according to the sixty-first aspect, in which the metal filmis made of at least one selected from the group consisting of Au, Pt,Ag, Ni, Ta, W, Pd, Mo, Ti, and Cr, and the metal oxide film is made ofat least one selected from the group consisting of ZrO₂, HfO₂, TiO₂,Ta₂O₅, SiO, and Cr₂O₃.

According to the exposure apparatus of any one of the sixtieth tosixty-second aspects, it is possible to prevent irradiation of theexposure light beam and reflected light of the exposure light beam froma wafer onto the sealing member formed in the peripheral portion of theside surface (the tapered surface) of the transmissive optical elementon the substrate's side of the projection optical system by use of thelight-shielding film. In this way, it is possible to preventdeterioration of the sealing member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a schematic configuration of a projectionexposure apparatus used in Embodiment 1.

FIG. 2 is a view showing a configuration of an optical element ofEmbodiment 1.

FIG. 3 is a view showing positional relations among a tip portion of theoptical element, and exhaust nozzles as well as intake nozzles in an Xdirection in terms of a projection optical system shown in FIG. 1.

FIG. 4 is a view showing positional relations among the tip portion ofthe optical element, and exhaust nozzles as well as intake nozzles in aY direction in terms of the projection optical system shown in FIG. 1.

FIG. 5 is an enlarged view of a substantial part in the projectionoptical system shown in FIG. 1, which illustrates aspects of supply andrecovery of a liquid to and from a space between the optical element inthe projection optical system and a wafer W.

FIG. 6 is a view showing a configuration of an optical element ofEmbodiment 3.

FIG. 7 is a view showing a configuration of an optical element ofEmbodiment 6.

FIG. 8 is a graph showing a relation between reflectivity and an exitangle in terms of the optical element of Embodiment 6 applied to an ArFexcimer laser.

FIG. 9 is a view showing a configuration of an optical element ofEmbodiment 7.

FIG. 10 is a graph showing a relation between reflectivity and an exitangle in terms of the optical element of Embodiment 7 applied to the ArFexcimer laser.

FIG. 11 is a view showing a configuration of an optical element ofEmbodiment 8.

FIG. 12 is a graph showing a relation between reflectivity and an exitangle in terms of the optical element of Embodiment 8 applied to the ArFexcimer laser.

FIG. 13 is a graph showing a relation between reflectivity and an exitangle θ in terms of the optical element of Embodiment 8 applied to theArF excimer laser when a film thickness of a second layer is reduced byhalf.

FIG. 14 is a view showing a configuration of an optical element ofEmbodiment 9.

FIG. 15 is a graph showing a relation between reflectivity and an exitangle in terms of the optical element of Embodiment 9 applied to the ArFexcimer laser.

FIG. 16 is a view showing a configuration of an optical element ofEmbodiment 10.

FIG. 17 is a graph showing a relation between reflectivity and an exitangle in terms of the optical element of Embodiment 10 applied to theArF excimer laser.

FIG. 18 is a view showing a configuration of an optical element ofEmbodiment 11.

FIG. 19 is a graph showing a relation between reflectivity and an exitangle in terms of the optical element of Embodiment 11 applied to theArF excimer laser.

FIG. 20 is a view showing a configuration of an optical element ofEmbodiment 12.

FIG. 21 is a graph showing a relation between reflectivity and an exitangle in terms of the optical element of Embodiment 12 applied to theArF excimer laser.

FIG. 22 is a view showing a configuration of an optical member used inEmbodiment 14.

FIG. 23 is a graph showing angle-reflectance characteristics on aninterface of optical contact shown in FIG. 22.

FIG. 24 is a view showing a configuration of an optical member used inEmbodiment 15.

FIG. 25 is a view showing a configuration of an optical element used inEmbodiment 16.

FIG. 26 is a view conceptually showing a first step in a manufacturingprocess for an optical element 4 shown in FIG. 25.

FIG. 27 is a view conceptually showing a second step in themanufacturing process for the optical element 4 shown in FIG. 25.

FIG. 28 is a view conceptually showing a third step in the manufacturingprocess for the optical element 4 shown in FIG. 25.

FIG. 29 is a view conceptually showing a fourth step in themanufacturing process for the optical element 4 shown in FIG. 25.

FIG. 30 is a view showing a schematic configuration of a projectionexposure apparatus used in Embodiment 17.

FIG. 31 is a view showing positional relations among a tip portion ofthe optical element, and exhaust nozzles as well as intake nozzles in anX direction in terms of a projection optical system shown in FIG. 30.

FIG. 32 is a view showing positional relations among the tip portion ofthe optical element, and exhaust nozzles as well as intake nozzles in aY direction in terms of the projection optical system shown in FIG. 30.

FIG. 33 is a view showing a schematic configuration of an exposureapparatus according to Embodiment 33.

FIG. 34 is a view showing a configuration of an optical elementaccording to Example 1.

FIG. 35 is a view showing an aspect of reflection when light is incidenton calcium fluoride.

FIG. 36 is a graph showing residual reflectivity of calcium fluoridewhen the light is incident on a calcium fluoride substrate.

FIG. 37 is a view showing a configuration of an experimental device usedin Example 1.

FIG. 38 is a view showing a configuration of an optical elementaccording to Example 2.

FIG. 39 is a view showing a configuration of an experimental device usedin Comparative Example 1.

FIG. 40 is a graph showing results of measurement of steps measuredafter the experiments of the optical elements of Comparative Example 1,Example 1, and Example 2.

FIG. 41 is a view showing a configuration of a transmissive opticalelement according to Example 3.

FIG. 42 is a view showing a configuration of a tester according toExample 3.

FIG. 43 is a view showing a configuration of a transmissive opticalelement according to Example 4.

FIG. 44 is a view showing a configuration of a transmissive opticalelement according to Example 5.

FIG. 45 is a view showing a configuration of an optical elementaccording to Example 6.

FIG. 46 is a view showing a configuration of an optical elementaccording to Example 7.

FIG. 47 is a view showing a configuration of a sample 1 used in Example6.

FIG. 48 is a view showing a configuration of a sample 2 used in Example7.

FIG. 49 is a view showing a configuration of a sample 3 used inReference Example 1.

FIG. 50 is a view showing an experimental device used in Examples 6 and7 and Reference Example 1.

FIG. 51 is a graph showing results of experiments in Examples 6 and 7and Reference Example 1.

FIG. 52 is a view showing the state of the sample 3 after theexperiment.

FIG. 53 is a view showing a configuration of a transmissive opticalelement according to Example 8.

FIG. 54 is a view showing a configuration of a transmissive opticalelement according to Example 10.

FIG. 55 is a view showing a configuration of a transmissive opticalelement according to Example 11.

FIG. 56 is a view showing a configuration of a transmissive opticalelement according to Reference Example 2.

FIG. 57 is a graph showing angle-reflectance characteristics when lightfrom a medium is incident on the transmissive optical elements accordingto Example 10 and Reference Example 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, preferred embodiments of the present invention will be describedwith reference to the accompanying drawings.

Embodiment 1

A projection exposure apparatus according to Embodiment 1 of thisinvention will now be described with reference to the accompanyingdrawings. FIG. 1 is a view showing a schematic configuration of aprojection exposure apparatus applying the step and repeat methodaccording to Embodiment 1. It is to be noted that an XYZ orthogonalcoordinate system as illustrated in FIG. 1 will be set up in thefollowing explanation, and positional relations of respective memberswill be described with reference to this XYZ orthogonal coordinatesystem. In terms of the XYZ orthogonal coordinate system, an X axis anda Y axis are set parallel to a wafer W while a Z axis is set in theorthogonal direction to the wafer W. In terms of the XYZ orthogonalcoordinate system in the figure, an XY plane is actually set to aparallel plane to a horizontal plane while the Z axis is set in thevertical direction.

As shown in FIG. 1, the projection exposure apparatus according to thisembodiment is provided with an illumination optical system 1 whichincludes an ArF excimer laser as an exposure light source, an opticalintegrator (a homogenizer), a field stop, a condenser lens, and thelike. Exposure light (an exposure light beam) IL consisting ofultraviolet pulse beams having a wavelength of 193 nm is emitted fromthe light source, then passes through the illumination optical system 1and thereby illuminates a pattern formed on a reticle (a mask) R. Thelight passing through the reticle R is reduced and projected onto anexposure region on the wafer (a substrate) W coated with a photoresistat given projection magnification β (β is set to ¼ or ⅕, for example)through a projection optical system PL which is rendered telecentric onboth sides (or on one side toward the wafer W).

Here, as the exposure light IL, it is also possible to use a KrF excimerlaser beam (having a wavelength of 248 nm), an F₂ laser beam (having awavelength of 157 nm), an i-line from a mercury lamp (having awavelength of 365 nm), and the like.

Meanwhile, the reticle R is retained on a reticle stage RST, and thereticle stage RST incorporates a mechanism for finely moving the reticlein the X direction, the Y direction, and the direction of rotation.Positions of the reticle stage RST in terms of the X direction, the Ydirection, and the direction of rotation are measured and controlled inreal time by a reticle laser interferometer (not shown).

Meanwhile, the wafer W is fixed onto a Z stage 9 by use of a waferholder (not shown). The Z stage 9 is fixed onto an XY stage 10configured to travel along the XY plane that is substantially parallelto an image plane of the projection optical system PL, and controls afocal position (a position in the Z direction) and a tilt angle of thewafer W. Positions of the Z stage 9 in terms of the X direction, the Ydirection, and the direction of rotation are measured and controlled inreal time by a wafer laser interferometer 13 applying a movable mirror12 located on the Z stage 9. Moreover, the XY stage 10 is placed on abase 11 and configured to control the X direction, the Y direction, andthe direction of rotation of the wafer W.

A main control system 14 included in this projection exposure apparatusadjusts the positions of the reticle R in terms of the X direction, theY direction, and the direction of rotation based on measurement valueswhich are measured with the reticle laser interferometer. Specifically,the main control system 14 transmits a control signal to the mechanismincorporated in the reticle stage RST, and adjusts the positions of thereticle R by finely moving the reticle stage RST.

Moreover, the main control system 14 adjusts the focal position (theposition in the Z direction) and the tilt angle of the wafer W in orderto align a surface of the wafer W with the image plane of the projectionoptical system PL by applying the auto-focus method and theauto-leveling method. Specifically, the main control system 14 adjuststhe focal position and the tilt angle of the wafer W by transmitting acontrol signal to a wafer stage drive system 15 and driving the Z stage9 with the wafer stage drive system 15. In addition, the main controlsystem 14 adjusts the positions of the wafer W in terms of the Xdirection, the Y direction, and the direction of rotation based onmeasurement values which are measured with the wafer laserinterferometer 13. Specifically, the main control system 14 adjusts thepositions and the direction of rotation of the wafer W by transmitting acontrol signal to the wafer stage drive system 15 and driving the XYstage 10 with the wafer stage drive system 15.

At the time of exposure, the main control system 14 sequentially movesrespective shot regions on the wafer W stepwise to a position ofexposure by transmitting a control signal to the wafer stage drivesystem 15 and driving the XY stage 10 with the wafer stage drive system15. Specifically, the main control system 14 repeats an operation forexposing a pattern image of the reticle R onto the wafer W in accordancewith the step and repeat method.

This projection exposure apparatus adopts the liquid immersion method inorder to virtually shorten an exposure wavelength and to improveresolution. Here, in the projection exposure apparatus of the liquidimmersion type adopting the liquid immersion method, a given liquid 7fills a space between a surface of the wafer W and a transmissiveoptical element 4 on the wafer W side of the projection optical systemPL at least during the transfer of the pattern image of the reticle Ronto the wafer W. The projection optical system PL includes a lensbarrel 3 for housing multiple optical elements made of silica glass orcalcium fluoride, which collectively constitute the projection opticalsystem PL. In this projection optical system PL, the transmissiveoptical element 4 located in the closest position to the wafer W is madeof calcium fluoride, and surfaces (a tip portion 4A on the wafer W sideand a tapered surface 4B (see FIG. 2)) of the transmissive opticalelement 4 are only allowed to contact the liquid 7. In this way,corrosion and other defects of the lens barrel 3 made of metal areavoided.

Here, the base material of the transmissive optical element 4 shown inFIG. 2 is made of calcium fluoride, and crystal orientation of a filmforming surface of the calcium fluoride is defined as a (111) plane.Moreover, a magnesium fluoride (MgF₂) film F1 and a silicon dioxide(SiO₂) film F2 collectively serving as an anti-dissolution film areformed at the tip portion 4A on the wafer W side of the transmissiveoptical element 4, or a portion where the exposure light passes through,by use of the vacuum vapor deposition method. In addition, anothersilicon dioxide (SiO₂) film F3 is formed thereon by use of a wet filmforming method.

Meanwhile, a tantalum (Ta) film F5 (F4) serving as a metalanti-dissolution film (which also functions as an adhesion reinforcingfilm) is formed on the tapered surface 4B of the transmissive opticalelement 4, or a portion where the exposure light does not pass through,by use of the sputtering method. In addition, a silicon dioxide (SiO₂)film F6 serving as an protective film for the metal anti-dissolutionfilm (a protective film for the anti-dissolution film) for protectingthe metal anti-dissolution film is formed on a surface of the metalanti-dissolution film (the anti-dissolution film) F5 by the wet filmforming method simultaneously with formation of the silicon dioxide(SiO₂) film F3. Here, the metal anti-dissolution film (theanti-dissolution film) F5 to be formed on the tapered surface 4B of thetransmissive optical element 4 has solubility in pure water equal to orbelow 2 ppt and packing density equal to or above 95%. Moreover, meanreflectance of the anti-dissolution film formed on the tip portion 4A ofthe transmissive optical element 4 is equal to or below 2% when an exitangle of the exposure light beam is set to 50 degrees.

The transmissive optical element 4 shown in FIG. 2 is for instancemanufactured by the following steps:

(i) a masking seal is attached to the tip portion 4A on the wafer W sideof the transmissive optical element 4, or the portion where the exposurelight passes through, so as to avoid attachment of the metalanti-dissolution film F5 which is supposed to be formed on the taperedsurface 4B of the transmissive optical element 4 or the portion wherethe exposure light does not pass through;(ii) The tantalum (Ta) film is deposited in the thickness of 200 nm onthe tapered surface 4B of the transmissive optical element 4 by use ofthe sputtering method to form the metal anti-dissolution film (alsofunctioning as the adhesion reinforcing film) F5;(iii) The masking seal attached to the tip portion 4A on the wafer Wside of the transmissive optical element 4 is peeled off;(iv) The magnesium fluoride (MgF₂) film F1 in the thickness of 15 nm andthe silicon dioxide (SiO₂) film F2 in the thickness of 300 nm are formedat the tip portion 4A on the wafer W side of the transmissive opticalelement 4 by use of the vacuum vapor deposition method;(v) The silicon dioxide (SiO₂) films F3 and F6 in the thickness of 130nm are simultaneously formed on the tantalum (Ta) film F5 serving as themetal anti-dissolution film that is formed on the tapered surface 4B ofthe transmissive optical element 4 and on the silicon dioxide (SiO₂)film F2 formed at the tip portion 4A on the wafer W side of thetransmissive optical element 4 by use of the wet film forming method,and then the films F3 and F6 are heated and sintered at 160° C.; and(vi) The silicon dioxide (SiO₂) film F6 formed on the tantalum (Ta) filmF5 serving as the metal anti-dissolution film functions as theprotective film for the metal anti-dissolution film for protecting themetal anti-dissolution film.

Meanwhile, pure water which is easily available in large quantity at asemiconductor manufacturing plant or the like is used as the liquid 7.Here, the pure water contains very low quantity of impurities and istherefore expected to exhibit a function to clean the surface of thewafer W.

FIG. 3 is a view showing positional relations among the tip portion 4Aand the tapered surface 4B on the wafer W side of the transmissiveoptical element 4 in the projection optical system PL, the wafer W, andtwo pairs of exhaust nozzles as well as intake nozzles configured tointerpose the tip portion 4A and the tapered surface 4B on the wafer Wside in the X direction. Meanwhile, FIG. 4 is a view showing positionalrelations among the tip portion 4A and the tapered surface 4B on thewafer W side of the transmissive optical element 4 in the projectionoptical system PL, and two pairs of exhaust nozzles as well as intakenozzles configured to interpose the tip portion 4A and the taperedsurface 4B on the wafer W side in the Y direction. The projectionexposure apparatus of this embodiment includes a liquid supply device 5for controlling supply of the liquid 7 and a liquid recovery device 6for controlling discharge of the liquid 7.

The liquid supply device 5 includes a tank (not shown) for the liquid 7,a booster pump (not shown), a temperature control device (not shown),and the like. Moreover, as shown in FIG. 3, an exhaust nozzle 21 ahaving an elongated tip portion along the +X direction of the tipportion 4A and the tapered surface 4B on the wafer W side is connectedto the liquid supply device 5 through a supply tube 21, and an exhaustnozzle 22 a having an elongated tip portion along the −X direction ofthe tip portion 4A and the tapered surface 4B on the wafer W side isalso connected thereto through a supply tube 22. Meanwhile, as shown inFIG. 4, an exhaust nozzle 27 a having an elongated tip portion along the+Y direction of the tip portion 4A and the tapered surface 4B on thewafer W side is connected to the liquid supply device 5 through a supplytube 27, and an exhaust nozzle 28 a having an elongated tip portionalong the −Y direction of the tip portion 4A and the tapered surface 4Bon the wafer W side is also connected thereto through a supply tube 28.The liquid supply device 5 adjusts the temperature of the liquid 7 byuse of the temperature control device, and supplies thetemperature-controlled liquid 7 onto the wafer W from at least oneexhaust nozzle out of the exhaust nozzles 21 a, 22 a, 27 a, and 28 athrough at least one supply tube out of the supply tubes 21, 22, 27, and28. Here, the temperature of the liquid 7 is set to substantially thesame degree as the temperature inside a chamber in which the projectionexposure apparatus of this embodiment is housed by use of thetemperature control device, for example.

The liquid recovery device 6 includes a tank (not shown) for the liquid7, a suction pump (not shown), and the like. Moreover, as shown in FIG.3, intake nozzles 23 a and 23 b each having a tip portion spread in the−X direction of the tapered surface 4B are connected to the liquidrecovery device 6 through a recovery tube 23, and intake nozzles 24 aand 24 b each having a tip portion spread in the +X direction of thetapered surface 4B are also connected thereto through a recovery tube24. Here, the intake nozzles 23 a, 23 b, 24 a, and 24 b are disposed inthe manner that are spread into fan shapes relative to an axis thatpasses through the center of the tip portion 4A on the wafer W side andis parallel to the X axis. Meanwhile, as shown in FIG. 4, intake nozzles29 a and 29 b each having a tip portion spread in the −Y direction ofthe tapered surface 4B are connected to the liquid recovery device 6through a recovery tube 29, and intake nozzles 30 a and 30 b each havinga tip portion spread in the +Y direction of the tapered surface 4B arealso connected thereto through a recovery tube 30. Here, the intakenozzles 29 a, 29 b, 30 a, and 30 b are disposed in the manner that arespread into fan shapes relative to an axis that passes through thecenter of the tip portion 4A on the wafer W side and is parallel to theY axis.

The liquid recovery device 6 recovers the liquid 7 from the wafer Wthrough at least one intake nozzle out of the intake nozzles 23 a, 23 b,24 a, 24 b, 29 a, 29 b, 30 a, and 30 b through at least one recoverytube out of the recovery tubes 23, 24, 29, and 30.

Next, methods of supplying and recovering the liquid 7 will bedescribed. When the wafer W is moved stepwise in a direction (the −Xdirection) of an arrow 25A indicated with a solid line in FIG. 3, theliquid supply device 5 supplies the liquid 7 to a space between the tipportion 4A as well as the tapered surface 4B on the wafer W side of thetransmissive optical element 4 and the wafer W through the supply tube21 and the exhaust nozzle 21 a. The liquid recovery device 6 recoversthe liquid 7, which is supplied from the liquid supply device 5 to thespace between the tip portion 4A as well as the tapered surface 4B onthe wafer W side and the wafer W, from the wafer W through the recoverytube 23 and the intake nozzles 23 a and 23 b. In this case, the liquid 7flows on the wafer W in a direction (the −X direction) of an arrow 25B,whereby the space between the wafer W and the transmissive opticalelement 4 is stably filled with the liquid 7.

On the other hand, when the wafer W is moved stepwise in a direction(the +X direction) of an arrow 26A indicated with a chain line in FIG.3, the liquid supply device 5 supplies the liquid 7 to the space betweenthe tip portion 4A as well as the tapered surface 4B on the wafer W sideof the transmissive optical element 4 and the wafer W through the supplytube 22 and the exhaust nozzle 22 a. The liquid recovery device 6recovers the liquid 7, which is supplied from the liquid supply device 5to the space between the tip portion 4A as well as the tapered surface4B on the wafer W side and the wafer W, through the recovery tube 24 andthe intake nozzles 24 a and 24 b. In this case, the liquid 7 flows onthe wafer W in a direction (the +X direction) of an arrow 26B, wherebythe space between the wafer W and the transmissive optical element 4 isstably filled with the liquid 7.

Meanwhile, when the wafer W is moved stepwise in the Y direction, theliquid 7 is supplied and recovered along the Y direction. Specifically,when the wafer W is moved stepwise in a direction (the −Y direction) ofan arrow 31A indicated with a solid line in FIG. 4, the liquid supplydevice 5 supplies the liquid 7 through the supply tube 27 and theexhaust nozzle 27 a. The liquid recovery device 6 recovers the liquid 7,which is supplied from the liquid supply device 5 to the space betweenthe tip portion 4A as well as the tapered surface 4B on the wafer W sideand the wafer W, through the recovery tube 29 and the intake nozzles 29a and 29 b. In this case, the liquid 7 flows on the exposure region in adirection (the −Y direction) of an arrow 31B, whereby the space betweenthe wafer W and the transmissive optical element 4 is stably filled withthe liquid 7.

On the other hand, when the wafer W is moved stepwise in the +Ydirection, the liquid supply device 5 supplies the liquid 7 through thesupply tube 28 and the exhaust nozzle 28 a. The liquid recovery device 6recovers the liquid 7, which is supplied from the liquid supply device 5to the space between the tip portion 4A on the wafer W side and thewafer W, through the recovery tube 30 and the intake nozzles 30 a and 30b. In this case, the liquid 7 flows on the exposure region in the +Ydirection, whereby the space between the wafer W and the transmissiveoptical element 4 is stably filled with the liquid 7.

Here, in addition to the nozzles configured to supply and recover theliquid 7 along the X direction and the Y direction, it is also possibleto provide nozzles for supplying and recovering the liquid 7 alongoblique directions, for example.

Next, methods of controlling an amount of supply and an amount ofrecovery of the liquid 7 will be described. FIG. 5 is a view showing thestate of supplying and recovering the liquid 7 to and from the spacebetween the optical element 4 constituting the projection optical systemPL and the wafer W. As shown in FIG. 5, when the wafer W is traveling inthe direction (the −X direction) of the arrow 25A, the liquid 7 suppliedfrom the exhaust nozzle 21 a flows in the direction (the −X direction)of an arrow 25B and is recovered by the intake nozzles 23 a and 23 b. Inorder to maintain a constant amount of the liquid 7 to fill the spacebetween the optical element 4 and the wafer W even when the wafer W istraveling, an amount of supply Vi (m³/s) and an amount of recovery Vo(m³/s) of the liquid 7 are set equal. Moreover, the amount of supply Viand the amount of recovery Vo of the liquid 7 are adjusted based on atraveling speed v of the XY stage 10 (the wafer W). Specifically, theamount of supply Vi and the amount of recovery Vo of the liquid 7 arecalculated by the following formula 1.

Vi=Vo=D·v·d  (Formula 1)

Here, D denotes a diameter (m) of the tip portion 4A of the opticalelement 4 as shown in FIG. 1. Meanwhile, v denotes the traveling speed(m/s) of the XY stage 10 and d denotes a working distance (m) of theprojection optical system PL. The speed v for moving the XY stage 10stepwise is set up by the main control system 14, while the values D andd are preset. Accordingly, the liquid 7 always fills the space betweenthe optical element 4 and the wafer W by calculating and adjusting theamount of supply Vi and the amount of recovery Vo of the liquid 7 basedon the formula 1.

Here, the working distance d of the projection optical system PL ispreferably set as narrow as possible so as to retain the liquid 7 stablybetween the optical element 4 and the wafer W. For example, the workingdistance d of the projection optical system PL may be set approximatelyequal to 2 mm.

According to the projection exposure apparatus of this Embodiment 1, itis possible to prevent dissolution of the optical element because theanti-dissolution film is formed on the surface of the optical element.Therefore, the optical element is prevented from dissolving in theliquid filling the space between the tip portion of the projectionoptical system and the substrate. As a result, it is not necessary toreplace the optical element frequently and it is possible to maintainhigh throughput of the exposure apparatus. Moreover, it is not necessaryto stop operation of the exposure apparatus in order to replace thecorroded optical element, and it is thereby possible to manufacture endproducts efficiently. In addition, the optical element does not dissolvein the liquid and it is thereby possible to maintain an opticalperformance of the projection optical system. Hence it is possible tostabilize the quality of the manufactured end products and to continueexposure in the optimal condition.

Moreover, according to the projection exposure apparatus of thisEmbodiment 1, the metal anti-dissolution film that also functions as theadhesion reinforcing film is formed on the tapered surface 4B of thetransmissive optical element 4 on the wafer W side of the projectionoptical system PL. Therefore, it is possible to attach the metalanti-dissolution film closely to the transmissive optical element 4.Meanwhile, since the silicon dioxide (SiO₂) film is formed on thesurface of the metal anti-dissolution film, it is possible to preventdamage on the soft metal anti-dissolution film having low abrasionresistance and thereby to protect the metal anti-dissolution film.Therefore, it is possible to prevent infiltration to and corrosion ofthe transmissive optical element 4 by the liquid 7 interposed betweenthe surface of the wafer W and the projection optical system PL, andthereby to maintain the optical performance of the projection opticalsystem PL. Moreover, it is possible to maintain the performance of theexposure apparatus because the transmissive optical element 4 does notdissolve in the liquid 7. In addition, it is not necessary to replacethe transmissive optical element 4 frequently. Therefore, it is possibleto maintain high throughput of the projection exposure apparatus.

Furthermore, the metal anti-dissolution film is formed on the taperedsurface 4B of the transmissive optical element 4, or in other words, ata portion where the exposure light beam IL does not pass through.Therefore, it is possible to continue exposure in the optimal conditionwithout shielding the exposure light beam IL by the metalanti-dissolution film formed on the surface of the transmissive opticalelement 4.

Meanwhile, a refractive index n of pure water relative to the exposurelight beam having the wavelength around 200 nm is approximately equal to1.44, whereby the ArF excimer laser beam having the wavelength of 193 nmbecomes 1/n times shorter on the wafer W, or in other words, is reducedto 134 nm. In this way, it is possible to obtain high resolution. Inaddition, a depth of focus is magnified by about n times, i.e. about1.44 times as compared to the depth of focus in the air. Accordingly,when it is only necessary to secure the same degree of the depth offocus as the case of using the exposure light beam in the air, it ispossible to increase the numerical aperture of the projection opticalsystem PL and thereby to improve the resolution as well.

Moreover, the projection exposure apparatus of this Embodiment 1includes the two pairs of exhaust nozzles and intake nozzles which aremutually inverted in the X direction and in the Y direction.Accordingly, it is possible to fill the space between the wafer and theoptical element stably with the liquid when moving the wafer in the +Xdirection, the −X direction, the +Y direction or the −Y direction.

Meanwhile, since the liquid flows on the wafer, it is possible to rinseoff a foreign object that may be attached onto the wafer by using theliquid. Moreover, since the liquid is adjusted to a given temperature bya liquid supply device, the temperature of the surface of the wafer isset to a constant temperature. Accordingly, it is possible to preventdegradation of alignment accuracy attributable to thermal expansion ofthe wafer caused in the course of exposure. Therefore, it is possible toprevent degradation of alignment accuracy attributable to thermalexpansion of the wafer even when there is a time difference betweenalignment and exposure as in the case of alignment in accordance withthe enhanced global alignment (EGA) method, for example.

Further, according to the projection exposure apparatus of thisEmbodiment 1, the liquid flows in the same direction as the direction ofmovement of the wafer. Therefore, it is possible to recover the liquidthat absorbs foreign objects and the heat by use of the liquid recoverydevice without accumulating the liquid on the exposure regionimmediately below the surface of the transmissive optical element.

In the above-described embodiment, the anti-dissolution film appliesmagnesium fluoride (MgF₂) and silicon dioxide (SiO₂). Instead, theanti-dissolution film may apply at least one of lanthanum fluoride(LaF₃), strontium fluoride (SrF₂), yttrium fluoride (YF₃), rutheniumfluoride (RuF₃), hafnium fluoride (HfF₄), neodymium fluoride (NdF₃),gadolinium fluoride (GdF₃), ytterbium fluoride (YbF₃), dysprosiumfluoride (DyF₃), aluminum fluoride (AlF₃), cryolite (Na₃AlF₆), chiolite(5NaF.3AlF₃), aluminum oxide (Al₂O₃), silicon dioxide (SiO₂), titaniumoxide (TiO₂), magnesium oxide (MgO), hafnium oxide (HfO₂), chromiumoxide (Cr₂O₃), zirconium oxide (ZrO₂), tantalum pentoxide (Ta₂O₅), andniobium pentoxide (Nb₂O₅).

Moreover, in the above-described embodiment, the anti-dissolution filmmade of magnesium fluoride (MgF₂) and silicon dioxide (SiO₂) is formedon the optical element by use of the vacuum vapor deposition method.Instead, the anti-dissolution film may be formed by use of at least oneof film forming methods out of an ion beam assisted vapor depositionmethod, a gas cluster ion beam assisted vapor deposition method, an ionplating method, an ion beam sputtering method, a magnetron sputteringmethod, a bias sputtering method, an electron cyclotron resonance (ECR)sputtering method, a radio frequency (RF) sputtering method, a thermalchemical vapor deposition (thermal CVD) method, a plasma enhanced CVDmethod, and a photo CVD method.

When forming a fluoride as the anti-dissolution film for the opticalelement, the optimal optical film forming method may be the vacuum vapordeposition method, the ion beam assisted vapor deposition method, thegas cluster ion beam assisted vapor deposition method or the ion platingmethod. However, in terms of magnesium fluoride (MgF₂) and yttriumfluoride (YF₃), it is possible to form such a film by use of thesputtering method. In the meantime, when forming an oxide film as theanti-dissolution film for the optical element, it is possible to applyall the film forming methods cited above.

Moreover, when calcium fluoride having a crystal orientation of (111)plane is used as a base material of the optical element, theanti-dissolution film to be formed thereon, or lanthanum fluoride (LaF₃)in particular, achieves heteroepitaxial growth when deposited on a filmforming surface thereof. In this case, the anti-dissolution film thusformed becomes extremely dense and constitutes a crystalline structurewith very few defects.

Furthermore, in the projection exposure apparatus according toEmbodiment 1, the metal film constructed as the film made of tantalum(Ta) is used as the metal anti-dissolution film (the anti-dissolutionfilm). Instead, it is possible to use a metal film constructed as a filmmade of at least one of gold (Au), platinum (Pt), silver (Ag), nickel(Ni), tungsten (W), palladium (Pd), molybdenum (Mo), titanium (Ti), andchromium (Cr).

Meanwhile, the projection exposure apparatus according to Embodiment 1applies the adhesion reinforcing film constructed as the film made oftantalum (Ta). Instead, it is possible to apply the adhesion reinforcingfilm constructed as a film made of chromium (Cr).

Moreover, the projection exposure apparatus of this Embodiment 1 appliesthe protective film for the metal anti-dissolution film (a protectivefilm for anti-dissolution film) constructed as the film made of silicondioxide (SiO₂). Instead, it is possible to apply the protective film forthe metal anti-dissolution film constructed as a film made of at leastone of yttrium oxide (Y₂O₃), neodymium fluoride (Nd₂F₃), chromium oxide(Cr₂O₃), tantalum pentoxide (Ta₂O₅), niobium pentoxide (Nb₂O₅), titaniumdioxide (TiO₂), zirconium dioxide (ZrO₂), hafnium dioxide (HfO₂), andlanthanum oxide (La₂O₃). In other words, it is possible to select theprotective film for the metal anti-dissolution film. Therefore, it ispossible to select the most appropriate protective film for the metalanti-dissolution film (the protective film for the anti-dissolutionfilm) based on the material of the transmissive optical element, theenvironment where the transmissive optical element is placed, the typeof the liquid interposed between the surface of the material and theprojection optical system, and the like.

Meanwhile, in the projection exposure apparatus of this Embodiment 1,the silicon dioxide (SiO₂) film serving as the anti-dissolution film aswell as the protective film for the metal anti-dissolution film isformed by use of the wet film forming method. Instead, it is possible toform the film by use of a dry film forming method such as the sputteringmethod.

Moreover, the metal anti-dissolution film (which also functions as theadhesion reinforcing film) and the protective film for the metalanti-dissolution film are formed on the tapered surface of thetransmissive optical element of this Embodiment 1. However, it is alsopossible to form only the metal anti-dissolution film (theanti-dissolution film). Alternatively, it is also possible to separatethe adhesion reinforcing film from the metal anti-dissolution film. Inother words, it is possible to form the adhesion reinforcing film andthe metal anti-dissolution film separately, or to form the adhesionreinforcing film, the metal anti-dissolution film, and the protectivefilm for the metal anti-dissolution film separately.

Furthermore, in the projection exposure apparatus of this Embodiment 1,the transmissive optical element 4 located closest to the wafer W ismade of calcium fluoride, and the adhesion reinforcing film, the metalanti-dissolution film (the anti-dissolution film), and the protectivefilm for the metal anti-dissolution film (the protective film for theanti-dissolution film) are formed on the tapered surface thereof.Instead, it is also possible to form the transmissive optical element 4located closest to the wafer W by use of fused silica, and then to formthe aforementioned films on the tapered surface thereof.

Meanwhile, in the above-described embodiment, the space between thesurface of the wafer and the optical element made of calcium fluorideand formed on the wafer's side of the projection optical system isfilled with the liquid. Instead, it is possible to interpose the liquidpartially between the surface of the wafer and the optical element madeof calcium fluoride and formed on the wafer's side of the projectionoptical system.

Moreover, although pure water is used as the liquid 7 in theabove-described embodiment, the liquid is not limited only to the purewater. It is also possible to use another material (such as cedar oil)for the liquid 7, which allows transmission of the exposure light beamand has a high refractive index as much as possible, and remains stableagainst the photoresist with which the projection optical system and thesurface of the wafer are coated.

Embodiment 2

A projection exposure apparatus is configured as similar to that ofEmbodiment 1 except that a magnesium fluoride (MgF₂) film is formed atthe tip portion 4A of the optical element 4, or in other words, at theportion contacting the liquid 7, as the single-layered anti-dissolutionfilm by use of the vacuum vapor deposition method.

According to the projection exposure apparatus of this Embodiment 2, thesingle-layered anti-dissolution film is formed on the surface of theoptical element, and it is thereby possible to prevent dissolution ofthe optical element. Further, it is possible to reduce the interface ascompared to the multilayer film. Therefore, it is possible to minimizean adverse effect attributable to a chemical reaction which is apt tooccur when the liquid infiltrates into the interface of the protectivelayer serving as the anti-dissolution film. Moreover, it is easier toform the film as compared to formation of the anti-dissolution filmincluding the multilayer film.

In addition, by forming the single-layered anti-dissolution film suchthat the refractive index of the optical element becomes equal to orlower than the refractive index of the liquid in the case of soaking thesurface of the optical element into the liquid, it is possible to obtainthe same optical performance as that of the optical element includingthe multilayer film.

Embodiment 3

A projection exposure apparatus is configured as similar to Embodiment 1except that the transmissive optical element 4 is modified as shown inFIG. 6 and as described below.

(i) The magnesium fluoride (MgF₂) film F1 is formed at the tip portion4A of the optical element 4 on the wafer W side, or in other words, atthe portion where the exposure light beam passes through, constituted ofthe single-layered anti-dissolution film by use of the vacuum vapordeposition method.(ii) The tantalum (Ta) film serving as the adhesion reinforcing film F4is formed on the tapered surface 4B of the transmissive optical element4, or in other words, at the portion where the exposure light beam doesnot pass through by use of the sputtering method. The adhesionreinforcing film F4 is used for improving adhesion between the taperedsurface 4B of the transmissive optical element 4 and the metalanti-dissolution film (the anti-dissolution film) F5 to be describedlater.(iii) A metal film made of gold (Au) is formed in the thickness of 150nm on the surface of the adhesion reinforcing film F4 as the metalanti-dissolution film (the anti-dissolution film) F5 for preventingdissolution in the liquid 7 by use of the sputtering method.(iv) A silicon dioxide (SiO₂) film is formed on the surface of the metalanti-dissolution film (the anti-dissolution film) F5 as the protectivefilm F6 for the metal anti-dissolution film (the protective film for theanti-dissolution film) for protecting the metal anti-dissolution film(the anti-dissolution film) by use of the sputtering method. Here, themetal anti-dissolution film (the anti-dissolution film) F5 to be formedon the tapered surface 4B of the transmissive optical element 4 hassolubility in pure water equal to or below 2 ppt and packing densityequal to or above 95%.

According to the projection exposure apparatus of this Embodiment 3, themetal film is formed on the surface of the adhesion reinforcing filmthat is formed on the tapered surface 4B of the transmissive opticalelement 4 on the wafer W side of the projection optical system PL.Therefore, it is possible to attach the metal film closely to thetransmissive optical element 4. Moreover, since the silicon dioxide(SiO₂) film is formed on the surface of the metal film, it is possibleto prevent damage on the soft metal film having low abrasion resistanceand thereby to protect the metal film. Therefore, it is possible toprevent infiltration to and corrosion of the transmissive opticalelement 4 by the liquid 7 interposed between the surface of the wafer Wand the projection optical system PL, and thereby to maintain theoptical performance of the projection optical system PL. Moreover, it ispossible to maintain the performance of the projection exposureapparatus because the transmissive optical element 4 does not dissolvein the liquid 7. In addition, it is not necessary to replace thetransmissive optical element 4 frequently. Therefore, it is possible tomaintain high throughput of the projection exposure apparatus.

Embodiment 4

A projection exposure apparatus is configured as similar to Embodiment 1except that magnesium fluoride (MgF₂) films are formed at the tipportion 4A and the side surface portion (the tapered portion) 4B of theoptical element 4, or in other words, at the portions contacting theliquid 7 as the anti-dissolution films.

According to the projection exposure apparatus of this Embodiment 4, theanti-dissolution films are formed on the surface on the substrate's sideof the optical element and on the side surface of the optical element,and it is thereby possible to prevent dissolution of the opticalelement. Further, the anti-dissolution films are formed on the surfaceon the substrate's side of the optical element and on the side surfaceof the optical element by use of an identical material. Accordingly, itis possible to form the anti-dissolution films at the same time, andthereby to form the anti-dissolution films by a simple process.

Embodiment 5

A projection exposure apparatus is configured as similar to Embodiment 1except that the transmissive optical element 4 is modified as describedbelow.

(i) A silicon dioxide (SiO₂) film is formed at the tip portion 4A on thewafer W side of the transmissive optical element 4, or in other words,at the portion where the exposure light beam passes through, as a firstfilm by use of the sputtering method which is a dry film forming method.(ii) Another silicon dioxide (SiO₂) film is formed on a surface of thefirst film as a second film by spin coating which is a wet film formingmethod.(iii) The tapered surface 4B of the transmissive optical element 4, orin other words, the portion where the exposure light beam does not passthrough is polished with a #2000 grind stone, for example, to increasesurface roughness and the surface area thereof. On the tapered surface4B subjected to the surface treatment of polishing with the grind stone,a silicon dioxide (SiO₂) film is formed as an anti-dissolution oxidefilm by spin coating which is the wet film forming method.

According to the projection exposure apparatus of this Embodiment 5, thesilicon dioxide (SiO₂) film is formed at the tip portion on the wafer Wside of the transmissive optical element, which is the portion of theprojection optical system that is located closest to the wafer, as thefirst film by use of the sputtering method. Meanwhile, the silicondioxide (SiO₂) film is formed on the surface of the first film as thesecond film by spin coating. Therefore, it is possible to attach thefirst film closely to the transmissive optical element made of calciumfluoride, and thereby possible to utilize the first film as the adhesionreinforcing layer to attach the transmissive optical element closely tothe second film.

Moreover, the second film is formed by use of the wet film formingmethod characterized by high homogeneity and a high filling performancerelative to voids. Therefore, it is possible to prevent infiltration toand corrosion of the transmissive optical element by the liquidinterposed between the surface of the wafer and the projection opticalsystem by eliminating the voids as a consequence of penetration of thesecond film into the voids on the first film. In this way, it ispossible to maintain the optical performance of the projection opticalsystem. Moreover, since both of the first film and the second film arethe silicon dioxide (SiO₂) films, bonding power between the first filmformed by the sputtering method and the second film formed by spincoating is strengthened, and it is thereby possible to attach the bothfilms more firmly. As a result, it is possible to avoid separation ofthe first film and the second film from the transmissive optical elementand to avoid dissolution of the transmissive optical element in theliquid. In this way, it is possible to maintain the performance of theexposure apparatus. In addition, it is not necessary to replace thetransmissive optical element frequently. Therefore, it is possible tomaintain high throughput of the exposure apparatus.

Moreover, the tapered surface of the transmissive optical element, whichis located closest to the wafer, of the projection optical system ispolished with a #2000 grind stone, for example, to increase the surfaceroughness and surface area thereof. On the tapered surface thuspolished, a silicon dioxide (SiO₂) film is formed as an anti-dissolutionoxide film by spin coating. Since the anti-dissolution oxide film isformed by use of the wet film forming method characterized by highhomogeneity and a high filling performance relative to voids, it ispossible to prevent infiltration to and corrosion of the transmissiveoptical element by the liquid, and thereby to maintain the opticalperformance of the projection optical system. As a result, it ispossible to avoid dissolution of the transmissive optical element in theliquid. In this way, it is possible to maintain the performance of theexposure apparatus. In addition, it is not necessary to replace thetransmissive optical element frequently. Therefore, it is possible tomaintain high throughput of the exposure apparatus.

Here, in the projection exposure apparatus of this Embodiment 5, thesilicon dioxide (SiO₂) film is formed at the tip portion 4A on the waferW side of the transmissive optical element 4, or in other words, at theportion where the exposure light beam passes through, as the first filmby use of the dry film forming method. Moreover, the silicon dioxide(SiO₂) film is formed on the surface of the first film as the secondfilm by use of the wet film forming method. Instead, it is possible toform the silicon dioxide (SiO₂) film as the anti-dissolution oxide filmat the tip portion 4A on the wafer's side of the transmissive opticalelement 4 by use of only the wet film forming method. In this case, thetip portion 4A of the transmissive optical element 4 is subjected to thesurface treatment to the extent not to degrade the optical performanceof the projection optical system PL in order to enhance adhesion betweenthe transmissive optical element 4 and the anti-dissolution oxide film.Specifically, the surface of the tip portion 4A is polished with a #2000grind stone, for example, so as to increase the surface roughness andthe surface area of the tip portion 4A.

Moreover, in the projection exposure apparatus of this Embodiment 5, thesilicon dioxide (SiO₂) film is formed on the tapered surface 4B of thetransmissive optical element 4, or in other words, the portion where theexposure light beam does not pass through, as the anti-dissolution oxidefilm, by use of only the wet film forming method. However it is possibleto form the silicon dioxide (SiO₂) film as the first film on the taperedsurface 4B by use of the dry film forming method and then to form thesilicon dioxide (SiO₂) film as the second film on the surface of thefirst film by use of the wet film forming method.

Embodiment 6

A projection exposure apparatus is configured as similar to Embodiment 1except applying the transmissive optical element 4 described below.

Specifically, FIG. 7 is a view showing a configuration of an opticalelement used in Embodiment 6 of the present invention. Here, an opticalelement 1 includes an optical substrate 101 and a multilayer film 100.The optical substrate 101 is made of calcium fluoride. Meanwhile, themultilayer film 100 has a four-layered structure including lanthanumfluoride (hereinafter expressed as LaF₃) as a first layer 102, magnesiumfluoride (hereinafter expressed as MgF₂) as a second layer 103, aluminumoxide (hereinafter expressed as Al₂O₃) as a third layer 104, and asilicon oxide (hereinafter expressed as SiO₂) as a fourth layer 105laminated in this order from the optical substrate 101 side. Animmersion liquid 108 is water and a substrate 107 is silicon coated witha photoresist.

Solubility of the fourth layer (SiO₂) 105 or the third layer (Al₂O₃) 104in water indicates the lower limit of a measuring instrument equal to1.0×10⁻⁷ grams per hundred grams of water. Therefore, the fourth layer(SiO₂) 105 and the third layer (Al₂O₃) 104 are substances that areinsoluble in water. Accordingly, the films made of these substances havea protective function against water.

Here, the vacuum vapor deposition method is used as the film formingmethod. It is to be noted, however, that the film forming method is notlimited only to this method. It is possible to apply various sputteringmethods, ion beam assisted methods, and ion plating methods that canproduce dense structures.

Refractive indices and optical film thicknesses based on a designeddominant wavelength λ of the first layer (LaF₃) 102, the second layer(MgF₂) 103, the third layer (Al₂O₃) 104, and the fourth layer (SiO₂) 105are shown in Table 1.

TABLE 1 Substance Refractive index Optical film thickness Immersionliquid water 1.44 — Fourth layer SiO₂ 1.55 0.12λ Third layer Al₂O₃ 1.850.54λ Second layer MgF₂ 1.43 0.66λ First layer LaF₃ 1.69 0.60λ Opticalsubstrate calcium 1.50 — fluoride

As shown in Table 1, it is apparent that the refractive indices of thefirst layer 102 and the third layer 104 being odd-numbered layers arehigher than the refractive indices of the calcium fluoride substrate101, the second layer 103, and the fourth layer 105 which are adjacentthereto. By forming the multilayer film 100 in the order shown in Table1 on the optical substrate 101, the multilayer film 100 has ananti-reflection function as a whole.

FIG. 8 is a graph showing a relation between reflectivity and an exitangle in terms of the optical element used in Embodiment 6 of thepresent invention in terms of the wavelength of 193 nm. An ArF (havingthe wavelength of 193 nm) excimer laser is applied hereto. As it isapparent from FIG. 8, mean reflectance Ra between S polarization Rs andP polarization Rp relative to incident light 20 is approximately equalto or below 0.3% even when the exit angle θ is equal to 40 degrees orapproximately equal to or below 0.5% even when the exit angle θ is equalto 50 degrees. Therefore, the optical element exhibits excellentcharacteristic and is usable enough.

Embodiment 7

A projection exposure apparatus is configured as similar to Embodiment 1except applying the transmissive optical element 4 described below.

FIG. 9 is a view showing a configuration of the optical element 1 of thepresent invention. Here, the optical element 1 includes the opticalsubstrate 101 and the multilayer film 100. The multilayer film 100 has athree-layered structure including lanthanum fluoride (hereinafterexpressed as LaF₃) as the first layer 102, magnesium fluoride(hereinafter expressed as MgF₂) as the second layer 103, and aluminumoxide (hereinafter expressed as Al₂O₃) as the third layer 104 laminatedin this order on the optical substrate 101. The immersion liquid 108 iswater and the substrate 107 is silicon coated with the photoresist.

Refractive indices and optical film thicknesses based on the designeddominant wavelength λ of the first layer (LaF₃) 102, the second layer(MgF₂) 103, and the third layer (Al₂O₃) 104 are shown in Table 2.

TABLE 2 Substance Refractive index Optical film thickness Immersionliquid water 1.44 — Third layer Al₂O₃ 1.85 0.54λ Second layer MgF₂ 1.430.66λ First layer LaF₃ 1.69 0.60λ Optical substrate calcium 1.50 —fluoride

As shown in Table 2, it is apparent that the refractive index of LaF₃ ofthe first layer 102 is higher than the refractive indices of the opticalsubstrate 101 and MgF₂ of the second layer 103 which are adjacentthereto. By arranging the refractive indices as described above, themultilayer film 100 has the anti-reflection function as a whole.

FIG. 10 is a graph showing a relation between reflectivity and an exitangle in terms of the optical element used in Embodiment 7 of thepresent invention in terms of the wavelength of 193 nm. The ArF (havingthe wavelength of 193 nm) excimer laser is applied hereto. As it isapparent from FIG. 10, the mean reflectance Ra between the Spolarization Rs and the P polarization Rp relative to the incident light20 is approximately equal to or below 0.3% even when the exit angle θ isequal to 40 degrees or approximately equal to or below 0.8% even whenthe exit angle θ is equal to 50 degrees. Therefore, the optical elementexhibits excellent characteristic and is usable enough.

Embodiment 8

A projection exposure apparatus is configured as similar to Embodiment 1except applying the transmissive optical element 4 described below.

FIG. 11 is a view showing a configuration of the optical element 1 ofthe present invention. Here, the optical element 1 includes the opticalsubstrate 101 and the multilayer film 100. The multilayer film 100 has atwo-layered structure including lanthanum fluoride (hereinafterexpressed as LaF₃) as the first layer 102 and magnesium fluoride(hereinafter expressed as MgF₂) as the second layer 103, which aresequentially laminated on the optical substrate 101. The immersionliquid 108 is water and the substrate 107 is silicon coated with thephotoresist.

Refractive indices and optical film thicknesses based on the designeddominant wavelength λ of the first layer (LaF₃) 102 and the second layer(MgF₂) 103 are shown in Table 3.

TABLE 3 Substance Refractive index Optical film thickness Immersionliquid water 1.44 — Second layer MgF₂ 1.43 0.60λ First layer LaF₃ 1.690.55λ Optical substrate calcium 1.50 — fluoride

As shown in Table 3, it is apparent that the refractive index of thefirst layer 102 is higher than the refractive indices of the opticalsubstrate 101 and MgF₂ of the second layer 103 which are adjacentthereto. By arranging the refractive indices as shown in Table 3, themultilayer film 100 has the anti-reflection function as a whole.

FIG. 12 is a graph showing a relation between reflectivity and an exitangle in terms of the optical element used in Embodiment 8 of thepresent invention in terms of the wavelength of 193 nm. The ArF (havingthe wavelength of 193 nm) excimer laser is applied hereto. As it isapparent from FIG. 12, the mean reflectance Ra between the Spolarization Rs and the P polarization Rp relative to the incident light20 is approximately equal to or below 0.3% when the exit angle θ isequal to 40 degrees or approximately equal to or below 2% even when theexit angle θ is equal to 50 degrees. Therefore, the optical element isusable enough.

Since the second layer (MgF₂) 103 has some solubility in water (2×10⁻⁴grams per hundred grams of water according to literature data) andtherefore dissolves in water when used over a long period of time.However, Embodiment 8 of the present invention applies water (therefractive index=1.44) and therefore has an advantage of relativelysmall variation in the optical performance even when the second layer(MgF₂) 103 is eluted.

FIG. 13 is a graph showing a relation between reflectivity and an exitangle θ of the optical element relative to the ArF (having thewavelength of 193 nm) excimer laser 10 when the film thickness of thesecond layer (MgF₂) 103 is reduced by half (0.3λ). As it is apparentfrom FIG. 13, the mean reflectance Ra between the S polarization Rs andthe P polarization Rp relative to the incident light 20 changes verylittle. Therefore, the optical element is usable enough. Accordingly, itis possible to use the optical element approximately for 10 years byforming the MgF₂ film 103 in the thickness of about 40 nm.

Although FIG. 11 is described by using the two-layered multilayer film100 including the first layer (LaF₃) 102 and the second layer (MgF₂)103, it is also possible to use a four-layer structured multilayer filmformed by alternately laminating the first layer (LaF₃) 102 and thesecond layer (MgF₂) 103.

Embodiment 9

A projection exposure apparatus is configured as similar to Embodiment 1except applying the transmissive optical element 4 described below.

FIG. 14 is a view showing a configuration of the optical element 1 ofthe present invention. This optical element 1 is formed by laminatingthe multilayer film 100 on the calcium fluoride substrate 101. Thismultilayer film 100 has a two-layered structure including MgF₂ as thefirst layer 102 and SiO₂ as the second layer 103, which are sequentiallylaminated on the optical substrate 101. The immersion liquid 108 iswater and the substrate 107 is silicon coated with the photoresist.

Here, refractive indices of the first layer (MgF₂) 102 and the secondlayer (SiO₂) 103, and optical film thicknesses as well as film thicknessranges of the respective layers 102 and 103 based on the designeddominant wavelength λ are shown below.

TABLE 4 Refractive Optical film Film thickness Substance index thicknessrange Immersion water 1.44 liquid Second layer SiO₂ 1.55 2.50λ1.50~4.00λ First layer MgF₂ 1.43 0.10λ 0.03~0.10λ Optical calcium 1.50substrate fluoride

Here, the vacuum vapor deposition method is used as the film formingmethod. It is to be noted, however, that the film forming method is notlimited only to this method. It is possible to apply various sputteringmethods, ion beam assisted methods, and ion plating methods that canproduce dense structures.

FIG. 15 is a graph showing a relation between reflectivity and an exitangle in terms of the optical element 1 of this Embodiment 9 relative tothe ArF (having the wavelength of 193 nm) excimer laser. As it isapparent from FIG. 15, the mean reflectance between the S polarizationand the P polarization relative to the incident light 20 isapproximately equal to or below 0.6% even when the exit angle θ is equalto 40 degrees or approximately equal to or below 1% even when the exitangle θ is equal to 60 degrees. Therefore, the optical element exhibitsexcellent characteristic and is usable enough.

As shown in Table 4, it is apparent that the refractive index of thefirst layer (MgF₂) 102 is lower than the refractive indices of theoptical substrate 101 and the second layer (SiO₂) 103 which are adjacentthereto. By arranging the refractive indices as described above, themultilayer film 100 has the anti-reflection function as a whole.

Embodiment 10

A projection exposure apparatus is configured as similar to Embodiment 1except applying the transmissive optical element 4 described below.

FIG. 16 is a view showing a configuration of the optical element 1 ofthe present invention. This optical element 1 is formed by laminatingthe multilayer film 100 on the calcium fluoride substrate 101. Thismultilayer film 100 includes MgF₂ as the first layer 102 and SiO₂ as thesecond layer 103. Moreover, this second layer 103 includes two separatelayers. Specifically, a separate first layer 103 a formed by use of thedry film forming method and a separate second layer 103 b formed by useof the wet film forming method are sequentially laminated. The immersionliquid 108 is water and the substrate 107 is silicon coated with thephotoresist.

Here, refractive indices of the first layer (MgF₂) 102, SiO₂ film formedby the dry method of the separate first layer 103 a, and SiO₂ filmformed by the wet method of the separate second layer 103 b, and opticalfilm thicknesses as well as film thickness ranges of the respectivelayers 102 and so forth based on the designed dominant wavelength λ areshown below.

TABLE 5 Optical Refractive film Film thickness Substance index thicknessrange Immersion water 1.44 liquid Second layer SiO₂ film 1.55 0.40λ0.40λ (constant) (separate formed by second layer) wet method Secondlayer SiO₂ film 1.55 2.10λ 1.15~3.60λ (separate first formed by layer)dry method First layer MgF₂ 1.43 0.10λ 0.03~0.10λ Optical calcium 1.50substrate fluoride

Here, the first layer 102 and the separate first layer 103 a are formedby use of the vacuum vapor deposition method. It is to be noted,however, that the film forming method is not limited only to thismethod. It is possible to apply other dry film forming methods includingvarious sputtering methods, ion beam assisted methods, and ion platingmethods.

It is known that a structure of a thin film varies in this dry filmforming method depending on conditions including a substrate heatingtemperature, a film deposition rate, and the like. In the case of astructure having insufficient density, there is an increasing risk ofpenetration of water into the film which may reach the calcium fluoridesubstrate 101. Since calcium fluoride dissolves in water, there is anincreasing risk of a loss of the desired optical performanceattributable to immersion in water. In general, it is known that a SiO₂film formed by the vacuum vapor deposition method at a low substrateheating temperature allows penetration of water or water vapor.

In this case, by providing the SiO₂ layer formed by the wet film formingmethod as the separate second layer 103 b, the SiO₂ layer formed by thewet film forming method enters into voids on the SiO₂ layer formed bythe dry film forming method, and the voids are thereby eliminated. Inthis way, it is possible to prevent infiltration to and corrosion of theoptical element 1 by the given immersion liquid 108 interposed betweenthe surface of the substrate 107 and the projection optical system PL,and thereby to maintain the optical performance of the projectionoptical system PL. As a result, when this optical element 1 is appliedto the projection exposure apparatus of the liquid immersion type, it ispossible to avoid detachment of the multilayer film 100 of the presentinvention from the calcium fluoride substrate 101 and to avoiddissolution of the optical element 1 in the liquid. In this way, it ispossible to maintain the performance of the projection exposureapparatus. In addition, it is not necessary to replace the opticalelement 1 frequently. Therefore, it is possible to maintain highthroughput of the projection exposure apparatus.

The SiO₂ layer formed by the wet film forming method, which serves asthe separate second layer 103 b, is formed by spin coating using aconventional SiO₂ solution. Here, a sol-gel silica solution is used asthe SiO₂ solution and the calcium fluoride substrate 101 is coated withthe solution while being rotated at a rotating speed in a range from1000 to 2000 revolutions per minute. The film thickness to be achievedby the coating process depends on conditions including the concentrationof the SiO₂ solution, the rotating speed of the calcium fluoridesubstrate 101 in the spin coating process, temperature, humidity, andthe like. Accordingly, by preparing an analytical curve concerning thefilm thickness in advance based on the concentration as a parameter, itis possible to obtain a desired film thickness afterwards.

Here, the film thickness of the SiO₂ layer formed by the wet filmforming method serving as the separate second layer 103 b is set to0.40λ (50 nm). However, the film thickness is not limited only to thisvalue. Nevertheless, it is necessary to pay attention to occurrence ofcracks attributable to membrane stress when coating in a large filmthickness such as 1.2λ (150 nm) or above. Moreover, after coating theSiO₂ layer formed by the wet film forming method serving as the separatesecond layer 103 b, an annealing process is performed in the air at 160°C. for 2 hours as a post treatment. This process is intended toevaporate alcohol which is a main solvent of the SiO₂ solution, and tosinter the SiO₂ layer itself formed by the wet film forming method.

FIG. 17 is a graph showing a relation between reflectivity and an exitangle in terms of the optical element 1 of this Embodiment 10 relativeto the ArF (having the wavelength of 193 nm) excimer laser. As it isapparent from FIG. 17, the mean reflectance between the S polarizationand the P polarization is approximately equal to or below 0.6% even whenthe exit angle θ is equal to 40 degrees or approximately equal to orbelow 1% even when the exit angle θ is equal to 60 degrees. Therefore,the optical element exhibits excellent characteristic and is usableenough.

Moreover, as shown in Table 5 described above, it is apparent that therefractive index of the first layer (MgF₂) 102 is lower than therefractive indices of the optical substrate 101 and the second layer(SiO₂) 103 which are adjacent thereto. By arranging the refractiveindices as described above, the multilayer film 100 has theanti-reflection function as a whole. Incidentally, although the secondlayer (SiO₂) 103 is composed of the separate first layer 103 a formed byuse of the dry film forming method and the separate second layer 103 bformed by use of the wet film forming method, these layers are made ofthe identical material and are therefore regarded as the single layerfrom the optical perspective.

Embodiment 11

A projection exposure apparatus is configured as similar to Embodiment 1except applying the transmissive optical element 4 described below.

FIG. 18 is a view showing a configuration of the optical element 1 ofthe present invention. This optical element 1 is formed by laminatingthe multilayer film 100 on the calcium fluoride substrate 101. Themultilayer film 100 has a four-layered structure including LaF₃ as thefirst layer 102, MgF₂ as the second layer 103, LaF₃ as the third layer104, and SiO₂ as the fourth layer 105, which are sequentially laminatedon the calcium fluoride substrate 101. The immersion liquid 108 is waterand the substrate 107 is silicon coated with the photoresist.

Here, refractive indices of LaF₃ in the first layer 102, MgF₂ in thesecond layer 103, LaF₃ in the third layer 104, and SiO₂ in the fourthlayer 105, and optical film thicknesses as well as film thickness rangesof the respective layers 102 and so forth based on the designed dominantwavelength λ are shown below.

TABLE 6 Refractive Optical film Film thickness Substance index thicknessrange Immersion water 1.44 liquid Fourth layer SiO₂ 1.55 0.37λ0.15~1.50λ Third layer LaF₃ 1.69 0.70λ 0.40~0.90λ Second layer MgF₂ 1.430.10λ 0.03~0.15λ First layer LaF₃ 1.69 0.11λ 0.03~0.20λ Optical calcium,1.50 substrate fluoride

Here, the vacuum vapor deposition method is used as the film formingmethod. It is to be noted, however, that the film forming method is notlimited only to this method. It is possible to apply various sputteringmethods, ion beam assisted methods, and ion plating methods that canproduce dense structures.

FIG. 19 is a graph showing a relation between reflectivity and an exitangle in terms of the optical element 1 of this Embodiment 11 relativeto the ArF (having the wavelength of 193 nm) excimer laser. As it isapparent from FIG. 19, the mean reflectance between the S polarizationand the P polarization is approximately equal to or below 0.3% even whenthe exit angle θ is equal to 50 degrees or approximately equal to orbelow 0.5% even when the exit angle θ is equal to 60 degrees. Therefore,the optical element exhibits excellent characteristic and is usableenough.

Moreover, as shown in Table 6 described above, it is apparent that therefractive index of the first layer (LaF₃) 102 is higher than therefractive indices of the optical substrate 101 and the second layer(MgF₂) 103 which are adjacent thereto. Meanwhile, it is also apparentthat the refractive index of the third layer (LaF₃) 104 is higher thanthe refractive indices of the second layer (MgF₂) 103 and the fourthlayer (SiO₂) 105 which are adjacent thereto. By arranging the refractiveindices as described above, the multilayer film 100 has theanti-reflection function as a whole.

Although SiO₂ of the fourth layer 105 is formed by use of the vacuumvapor deposition method in this Embodiment 11, it is also possible toform this film by use of the wet film forming method as similar to theseparate second layer 103 b as described in Embodiment 5. In this case,by providing the SiO₂ layer formed by the wet film forming method, theSiO₂ layer formed by the wet film forming method enters the voids on thethird layer (LaF₃) 104 formed by use of the dry film forming method, andthe voids are thereby eliminated. In this way, it is possible to preventinfiltration to and corrosion of the optical element 1 by the givenimmersion liquid 108 interposed between the surface of the substrate 107and the projection optical system PL, and thereby to maintain theoptical performance of the projection optical system PL. As a result,when this optical element 1 is applied to the projection exposureapparatus of the liquid immersion type, it is possible to avoiddetachment of the multilayer film 100 of the present invention from thecalcium fluoride substrate 101 and to avoid dissolution of the opticalelement 1 in the liquid. In this way, it is possible to maintain theperformance of the projection exposure apparatus. In addition, it is notnecessary to replace the optical element 1 frequently. Therefore, it ispossible to maintain high throughput of the projection exposureapparatus.

Embodiment 12

A projection exposure apparatus is configured as similar to Embodiment 1except applying the transmissive optical element 4 described below.

FIG. 20 is a view showing a configuration of the optical element 1 ofthe present invention. This optical element 1 is formed by laminatingthe multilayer film 100 on the calcium fluoride substrate 101. Themultilayer film 100 has a five-layered structure including LaF₃ as thefirst layer 102, MgF₂ as the second layer 103, LaF₃ as the third layer104, MgF₂ as the fourth layer 105, and SiO₂ as a fifth layer 106, whichare sequentially laminated on the calcium fluoride substrate 101. Theimmersion liquid 108 is water and the substrate 107 is silicon coatedwith the photoresist.

Here, refractive indices of LaF₃ in the first layer 102, MgF₂ in thesecond layer 103, LaF₃ in the third layer 104, MgF₂ in the fourth layer105, and SiO₂ in the fifth layer 106, and optical film thicknesses aswell as film thickness ranges of the respective layers 102 and so forthbased on the designed dominant wavelength λ are shown below.

TABLE 7 Refractive Optical film Film thickness Substance index thicknessrange Immersion water 1.44 liquid Fifth layer SiO₂ 1.55 0.20λ 0.05~0.35λFourth layer MgF₂ 1.43 0.10λ 0.03~0.18λ Third layer LaF₃ 1.69 0.70λ0.55~0.82λ Second layer MgF₂ 1.43 0.10λ 0.03~0.18λ First layer LaF₃ 1.690.11λ 0.03~0.20λ Optical calcium 1.50 substrate fluoride

Here, the vacuum vapor deposition method is used as the film formingmethod. It is to be noted, however, that the film forming method is notlimited only to this method. It is possible to apply various sputteringmethods, ion beam assisted methods, and ion plating methods that canproduce dense structures.

FIG. 21 is a graph showing a relation between reflectivity and an exitangle in terms of the optical element of Embodiment 12 relative to theArF (having the wavelength of 193 nm) excimer laser. As it is apparentfrom FIG. 21, the mean reflectance between the S polarization and the Ppolarization is approximately equal to or below 0.3% even when the exitangle θ is equal to 50 degrees or approximately equal to or below 0.5%even when the exit angle θ is equal to 60 degrees. Therefore, theoptical element exhibits excellent characteristic and is usable enough.

Moreover, as shown in Table 7 described above, it is apparent that therefractive index of the first layer (LaF₃) 102 is higher than therefractive indices of the optical substrate 101 and the second layer(MgF₂) 103 which are adjacent thereto. Meanwhile, it is also apparentthat the refractive index of the third layer (LaF₃) 104 is higher thanthe refractive indices of the second layer (MgF₂) 103 and the fourthlayer (MgF₂) 105 which are adjacent thereto. By arranging the refractiveindices as described above, the multilayer film 100 has theanti-reflection function as a whole.

Although SiO₂ of the fifth layer 106 is formed by use of the vacuumvapor deposition method in this Embodiment 12, it is also possible toform this film by use of the wet film forming method as similar to theseparate second layer 103 b as described in Embodiment 10. In this case,by providing the SiO₂ layer formed by the wet film forming method, theSiO₂ layer formed by the wet film forming method enters the voids on thefourth layer (MgF₂) 105 formed by use of the dry film forming method,and the voids are thereby eliminated. In this way, it is possible toprevent infiltration to and corrosion of the optical element 1 by thegiven immersion liquid 108 interposed between the surface of thesubstrate 107 and the projection optical system PL, and thereby tomaintain the optical performance of the projection optical system PL. Asa result, when this optical element 1 is applied to the projectionexposure apparatus of the liquid immersion type, it is possible to avoiddetachment of the multilayer film 100 of the present invention from thecalcium fluoride substrate 101 and to avoid dissolution of the opticalelement 1 in the liquid. In this way, it is possible to maintain theperformance of the projection exposure apparatus. In addition, it is notnecessary to replace the optical element 1 frequently. Therefore, it ispossible to maintain high throughput of the projection exposureapparatus.

Embodiment 13

A projection exposure apparatus is configured as similar to Embodiment 1except applying the transmissive optical element 4 described below.

In this Embodiment 13, the material of the fourth layer 105 is differentfrom that used in Embodiment 12. Specifically, in This Embodiment 13,Al₂O₃ is formed as the fourth layer 105.

Here, refractive indices of LaF₃ in the first layer 102, MgF₂ in thesecond layer 103, LaF₃ in the third layer 104, Al₂O₃ in the fourth layer105, and SiO₂ in the fifth layer 106, and optical film thicknesses aswell as film thickness ranges of the respective layers 102 and so forthbased on the designed dominant wavelength λ are shown below.

TABLE 8 Refractive Optical film Film thickness Substance index thicknessrange Immersion water 1.44 liquid Fifth layer SiO₂ 1.55 0.37λ 0.28~0.55λFourth layer Al₂O₃ 1.85 0.10λ 0.03~0.18λ Third layer LaF₃ 1.69 0.51λ0.38~0.65λ Second layer MgF₂ 1.43 0.10λ 0.03~0.20λ First layer LaF₃ 1.690.11λ 0.03~0.25λ Optical calcium 1.50 substrate fluoride

Here, the vacuum vapor deposition method is used as the film formingmethod. It is to be noted, however, that the film forming method is notlimited only to this method. It is possible to apply various sputteringmethods, ion beam assisted methods, and ion plating methods that canproduce dense structures.

In this Embodiment 13, the mean reflectance between the S polarizationand the P polarization is approximately equal to or below 0.3% even whenthe exit angle θ is equal to 50 degrees or approximately equal to orbelow 0.5% even when the exit angle θ is equal to 60 degrees as similarto that of Embodiment 12. Therefore, the optical element exhibitsexcellent characteristic and is usable enough.

Moreover, as shown in Table 8, it is apparent that the refractive indexof the first layer (LaF₃) 102 is higher than the refractive indices ofthe optical substrate 101 and the second layer (MgF₂) 103 which areadjacent thereto. Meanwhile, it is also apparent that the refractiveindex of the third layer (LaF₃) 104 is higher than the refractiveindices of the second layer (MgF₂) 103 and the fourth layer (Al₂O₃) 105which are adjacent thereto. By arranging the refractive indices asdescribed above, the multilayer film 100 has the anti-reflectionfunction as a whole.

Although SiO₂ of the fifth layer 106 is formed by use of the vacuumvapor deposition method in this Embodiment 13, it is also possible toform this film by use of the wet film forming method as similar to theseparate second layer 103 b as described in Embodiment 10. In this case,by providing the SiO₂ layer formed by the wet film forming method, theSiO₂ layer formed by the wet film forming method enters the voids on thefourth layer (Al₂O₃) 105 formed by use of the dry film forming method,and the voids are thereby eliminated. In this way, it is possible toprevent infiltration to and corrosion of the optical element 1 by thegiven immersion liquid 108 interposed between the surface of thesubstrate 107 and the projection optical system PL, and thereby tomaintain the optical performance of the projection optical system PL. Asa result, when this optical element 1 is applied to the projectionexposure apparatus of the liquid immersion type, it is possible to avoiddetachment of the multilayer film 100 of the present invention from thecalcium fluoride substrate 101 and to avoid dissolution of the opticalelement 1 in the liquid. In this way, it is possible to maintain theperformance of the projection exposure apparatus. In addition, it is notnecessary to replace the optical element 1 frequently. Therefore, it ispossible to maintain high throughput of the projection exposureapparatus.

According to the projection exposure apparatus of any of theabove-described Embodiments 6 to 13, the multilayer film is formed onthe surface of the optical element and the multilayer film has theprotective function to protect the optical element against the liquidand an anti-reflection function to prevent reflection of the exposurelight beam (the incident light). Therefore, it is possible to providethe stable optical element without being corroded by the liquid. Henceit is possible to provide the optical element which can realize ahigh-performance projection exposure apparatus having high resolutionand large depth of focus by use of the liquid immersion method.Moreover, the multilayer film has the protective function for a giventime period, and is therefore capable of protecting the optical elementagainst water as the immersion liquid for ten years, for example. Henceit is possible to provide the optical element which can realize ahigh-performance projection exposure apparatus having high resolutionand large depth of focus by use of the liquid immersion method. At thesame time, it is possible to provide the stable optical element withoutbeing corroded by the liquid for the given time period.

Embodiment 14

A projection exposure apparatus is configured as similar to Embodiment 1except applying the transmissive optical element 4 described below.

FIG. 22 is a view showing a configuration of an optical member used inEmbodiment 14 of the present invention. The optical member 1 is formedby joining a fused silica thin plate 102 onto an optical element 101made of calcium fluoride. Here, an immersion liquid 103 is water and asubstrate is a silicon substrate 104 coated with photoresist. As for thejoining method, when the exposure wavelength corresponds to that ofultraviolet rays such as the ArF laser, two composition surfaces areformed into planar surfaces and subjected to optical contact. Theoptical contact means a phenomenon of virtual contact of solids owing toan intermolecular force, which is observed by attaching two planarsurfaces closely to each other. From the optical point of view, there isonly an interface between a solid and another solid.

If it is not possible to obtain desired adhesion due to poor planeaccuracy of the two interfaces subject to the optical contact, it isalso possible to enhance adhesion by slightly coating pure water in aspace between the interfaces to the extent not to cause corrosion on thesurface of the optical element 101. Refractive indices of the opticalelement 101 and the fused silica thin plate 102 are 1.50 and 1.55,respectively.

FIG. 23 is a graph showing an angle-reflectance characteristics on aninterface of optical contact (the fused silica/calcium fluoride) shownin FIG. 22. As it is apparent from FIG. 23, the mean reflectance Rabetween the S polarization Rs and the P polarization Rp relative to theincident light 20 is equal to or below 0.3% even when the exit angle θis equal to 60 degrees. Therefore, the optical member exhibits excellentcharacteristic and is usable enough.

The reason why the optical element 101 as the optical substrate is notmade of fused silica is that the fused silica thin plate 102 may causecompaction upon laser irradiation and is not therefore suitable. On theother hand, the reason for adopting the fused silica thin plate 102 isthat it is possible to minimize an adverse effect even if the compactionoccurs therein.

According to the projection exposure apparatus of the above-describedEmbodiment 14, the fused silica thin plate 102 has a very low solubilityin water and is therefore applicable without causing degradation in theperformance attributable to corrosion. It is possible to realize aliquid immersion optical system without causing optical degradation byusing this element for the liquid immersion method.

Embodiment 15

A projection exposure apparatus is configured as similar to Embodiment 1except applying the transmissive optical element 4 described below.

FIG. 24 is a view showing a configuration of the optical member used inEmbodiment 15 of the present invention. The optical member 1 is formedby joining a crystalline magnesium fluoride (hereinafter expressed asMgF₂) thin plate 105 onto the optical element 101 made of calciumfluoride. Here, the immersion liquid 103 is water and the substrate isthe silicon substrate 104 coated with photoresist. A space between theoptical element 101 and the MgF₂ thin plate 105 is filled with a liquid(a filler liquid) 106 with a small difference in refractive indextherefrom. If this filler liquid 106 has a difference in the refractiveindex equal to or below 0.2 relative to those of respective substrates,the filler liquid has small residual reflection and can be usedfavorably.

Since MgF₂ has some solubility in water (2×10⁻⁴ grams per hundred gramsof water according to the literature data) and therefore dissolves inwater when used over a long period of time. As the dissolutionprogresses, there is a risk of damaging a transmission wavefront of aprojector lens. If the optical element 101 is directly coated with amagnesium fluoride (MgF₂) which is in an inappropriate film thickness,there is the risk of distorting the transmission wavefront due to theelution. In this event, it may be necessary to carry out an extensiveoperation for replacing the optical element 101. Particularly, when theoptical element 101 is formed into a lens shape, it is necessary toperform delicate alignment with an optical axis of the projector lensupon replacement which is not easy. In the case of Embodiment 15 of thepresent invention, it is possible to replace only the thin plate.Accordingly, it is possible to perform replacement while minimizing anadverse effect on an image-forming performance.

Although Embodiment 15 of the present invention applies the crystallinemagnesium fluoride (MgF₂) thin plate, it is also possible to apply acrystalline magnesium fluoride (MgF₂) sintered body instead.Alternatively, it is also possible to apply a calcium fluoride thinplate coated with magnesium fluoride (MgF₂) or a very thin PTFE(polytetrafluoroethylene or Teflon (registered trademark)) thin plate.As for the coating method in this case, it is possible to apply not onlya typical vapor deposition method but also any appropriate methodsincluding ion plating method and various sputtering methods.

Here, the thin plate described in the description of the preferredembodiments of the present invention may be formed into a parallel plateas well.

According to the projection exposure apparatus of the above-describedEmbodiment 15, the tip portion of the projection optical system is notcorroded by the liquid. Therefore, it is not necessary to stop operationof the projection exposure apparatus in order to replace the opticalmember 1 corroded by water or the like, and it is thereby possible tomanufacture end products efficiently. Moreover, the optical member 1 ofthe present invention is not corroded for a given period of time whilethe projection exposure apparatus is in operation. Accordingly, theoptical member 1 has a stable optical characteristic. In this way, it ispossible to stabilize the quality of end products to be manufactured byuse of the projection exposure apparatus embedding the optical member ofthe present invention.

Although the present invention has been described with reference toEmbodiments 1 to 15, it should be understood that the present inventionis not limited only to the features described in Embodiments 1 to 15.For example, in Embodiment 4 and the like, the anti-dissolution filmsare formed on the surface on the substrate's side and on the sidesurface of the optical element on the substrate's side of the projectionoptical system by use of magnesium fluoride (MgF₂) as theanti-dissolution films. Instead, it is possible to form ananti-dissolution film on the surface on the substrate's side of theoptical element on the substrate's side of the projection optical systemby use of hydrophilic silicon oxide (SiO₂), and meanwhile, to form ahydrophobic anti-dissolution film on the side surface of the opticalelement on the substrate's side of the projection optical system by useof alkyl ketene dimer.

Here, the anti-dissolution film formed on the side surface of theoptical element is the anti-dissolution film having an excellenthydrophobic performance as compared to the anti-dissolution film formedon the surface on the substrate's side of the optical element, while theanti-dissolution film formed on the surface on the substrate's side ofthe optical element is the anti-dissolution film having an excellenthydrophilic performance as compared to the anti-dissolution film formedon the side surface of the optical element. It is possible to guide theliquid attached to the side surface of the optical element easily to thesubstrate's side because the anti-dissolution film formed on the sidesurface of the optical element is the hydrophobic anti-dissolution film.Moreover, it is possible to fill the space between the surface on thesubstrate's side of the optical element and the substrate constantlywith the liquid because the anti-dissolution film formed on the surfaceon the substrate's side of the optical element is the hydrophilicanti-dissolution film.

Meanwhile, in the above-described Embodiment 5 and the like, the firstfilm constructed as the silicon dioxide (SiO₂) film is formed on thetransmissive optical element by use of the sputtering method. Instead,it is possible to form this film by use of a different dry film formingmethod such as the vacuum vapor deposition method or the CVD method.

Moreover, in the above-described Embodiment 5 and the like, the silicondioxide (SiO₂) film is formed as the first film by use of the dry filmforming method and the other silicon dioxide (SiO₂) film is formed asthe second film by use of the wet film forming method. Instead, it ispossible to form the magnesium fluoride (MgF₂) film as the first film byuse of the dry film forming method and to form the silicon dioxide(SiO₂) film as the second film by use of the wet film forming method.

Meanwhile, in the above-described embodiments, the space between thesurface of the wafer and the optical element made of calcium fluorideand formed on the wafer's side of the projection optical system isfilled with the liquid. Instead, it is possible to interpose the liquidpartially between the surface of the wafer and the optical element madeof calcium fluoride and formed on the wafer's side of the projectionoptical system.

Moreover, although pure water is used as the liquid in theabove-described embodiments, the liquid is not limited only to the purewater. It is also possible to use another liquid (such as cedar oil),which allows transmission of the exposure light beam and has a highrefractive index as much as possible, and remains stable against thephotoresist with which the projection optical system and the surface ofthe wafer are coated. When a F₂ laser beam is used as the exposure lightbeam, it is possible to use a fluorinated liquid that allowstransmission of the F₂ laser beam. Such a fluorinated liquid may befluorinated oil or perfluoropolyether (PFPE), for example.

Moreover, in the above-described embodiments, the optical element usedin the present invention is formed into a lens shape. However, the shapeof the optical element is not limited only to the lens shape. Forexample, it is also possible to form the optical element of the presentinvention by forming a film on a calcium fluoride plate substrate as acover glass in a space between a conventional calcium fluoride lens andthe liquid.

In addition, Embodiments 14 and 15 explain the example of slightlycoating pure water on the two joining interfaces. Instead, it ispossible to use fluorinated solvents such as perfluorocarbon (PFC),hydrofluoroether (HFE) or perfluoropolyether (PFPE).

Moreover, the number and shapes of the nozzles used in the embodimentsare not particularly limited. For example, it is possible to provide twopairs of nozzles along a long side of the tip portion 4A to performsupply and recovery of the liquid. In this case, it is also possible toarrange the exhaust nozzles and the intake nozzles vertically so as toeffectuate the supply and recovery of the liquid both in the +Xdirection and in the −X direction.

Embodiment 16

A projection exposure apparatus is configured as similar to Embodiment 1except applying an optical element with which an optical memberoptically contacts through a film as described below.

As shown in FIG. 1, the projection exposure apparatus of this Embodiment16 applying the step and repeat method includes an illumination opticalsystem 1 for illuminating a reticle (a mask) R, a reticle stage deviceRST for supporting the reticle R, a wafer stage device for supporting awafer (a substrate) W, a wafer stage drive system 15 for driving thewafer stage device and thereby moving the wafer W three-dimensionally, aprojection optical system PL for projecting a pattern image formed onthe reticle R onto the wafer W, a liquid circulation device forsupplying a liquid 7 to a space between the projection optical system PLand the wafer W, and a main control system 14 for comprehensivelycontrolling overall operation of the projection exposure apparatus.

The illumination optical system 1 includes an ArF excimer laser as anexposure light source, an optical integrator (a homogenizer), a fieldstop, a condenser lens, and the like. An exposure light beam ILconsisting of ultraviolet pulse beams having a wavelength of 193 nm isemitted from the light source, and then passes through the illuminationoptical system 1 and thereby illuminates the pattern image provided onthe reticle R. The imaging light passing through the reticle R isprojected onto an exposure region on the wafer W coated with aphotoresist through a projection optical system PL. Here, as theexposure light beam IL, it is also possible to use the KrF excimer laserbeam (having the wavelength of 248 nm), the F₂ laser beam (having thewavelength of 157 nm), the i-line from a mercury lamp (having thewavelength of 365 nm), and the like.

The reticle stage device RST is configured to be capable of adjustingthe position and posture of the reticle R while retaining the reticle R.Specifically, the reticle stage device RST incorporates a mechanism forfinely moving the reticle R in an X direction and a Y direction whichare substantially perpendicular to an optical axis AX of the projectionoptical system PL, and in a direction of rotation around the opticalaxis AX. Positions of the reticle R in terms of the X direction, the Ydirection, and the direction of rotation are measured in real time by areticle laser interferometer (not shown) and are controlled by a reticlestage drive system (not shown).

The wafer stage device is configured to be capable of adjusting theposition and posture of the wafer W while retaining the wafer W. To bemore precise on the structure, the wafer W is fixed onto a Z stage 9 byuse of a wafer holder, and this Z stage 9 allows adjustment of a focalposition of the wafer W, i.e. a position in a Z direction substantiallyparallel to the optical axis AX, and a tilt angle thereof correspondingto that position. The Z stage 9 is fixed onto an XY stage 10 and this XYstage 10 is supported on a base 11. The XY stage 10 is capable of movingthe wafer holder along the XY plane that is substantially parallel to animage plane of the projection optical system PL, changing a shot regionon the wafer W, and so on. Here, positions of the Z stage 9 in terms ofthe X direction, the Y direction, and the direction of rotation aremeasured in real time by a movable mirror 12 located on the wafer holderand by a wafer laser interferometer 13 configured to supply measuringlight to the movable mirror 12.

The wafer stage drive system 15 is operated in response to a controlsignal from the main control system 14, and is capable of moving thewafer W to a target position at appropriate timing while retaining theposture in a desired condition.

The projection optical system PL includes a lens barrel 3 for housingmultiple optical elements such as lenses or optical components formed byprocessing silica glass or calcium fluoride. This projection opticalsystem PL is an image-forming optical system rendered telecentric onboth sides or on one side toward the wafer W. The pattern image on thereticle R is reduced and projected onto a shot region on the wafer W atgiven projection magnification β of ¼ or ⅕, for example, through theprojection optical system PL.

Here, this projection optical system PL constitutes a liquid immersionoptical system to be used in the state of filling the given liquid 7 ina space defined with the wafer W. In other words, this projectionexposure apparatus adopts the liquid immersion method in order tovirtually shorten an exposure wavelength and to improve resolution. Inthe projection exposure apparatus of the liquid immersion type, theliquid 7 fills a space between a surface of the wafer W and tip surfaceof an optical element 4 exposed on the wafer W side of the projectionoptical system PL at least during the transfer of the pattern image ofthe reticle R onto the wafer W. Pure water which is easily available inlarge quantity at a semiconductor manufacturing plant or the like isused as the liquid 7. Here, the pure water contains very low quantity ofimpurities and is therefore expected to exhibit a function to clean thesurface of the wafer W. Here, in the course of exposure, only the tipportion on the wafer W side of the optical element 4 out of theprojection optical system PL is configured to contact the liquid 7. Inthis way, corrosion and other defects of the lens barrel 3 made of metalare prevented.

FIG. 25 is a sectional side view for conceptually explaining a structureof the optical element 4, which protrudes toward the wafer W of theprojection optical system PL used in this embodiment.

As it is apparent from FIG. 25, the optical element 4 is formed byestablishing optical contact between a substrate member 201 which is theoptical element made of calcium fluoride and an optical member 202formed of a substrate member made of synthetic silica. In thisprojection optical system PL, only the optical member 202 on the tipside of the optical element 4 contact the liquid 7 which is pure wateror the like, while the substrate member 201 located in the back does notdirectly contact the liquid 7. The reason why the tip of the projectionoptical system PL is covered with the optical member 202 is that theoptical element 4 made of calcium fluoride has slight solubility in theliquid 7 which is pure water or the like. Accordingly, the opticalmember 202 made of synthetic silica having high water resistance isprovided for protecting the optical element 4.

When the optical member 202 is retained and fixed onto the opticalelement 4 by use of the optical contact, it is necessary to increasebond strength between the optical element 4 and the optical member 202so that the optical member 202 is not misaligned to or detached from theoptical element 4. For this reason, a thin coating film 203 made of anoxide is formed on a surface of the side of the substrate member 201 ofthe optical element 4 used for the optical contact. On the other hand,no coating film is formed on a surface of the side of the optical member202 used for the optical contact. As described above, the bond strengthbetween the substrate member 201 and the optical member 202 of theoptical element 4 is enhanced by interposing the coating film 203between the substrate member 201 and the optical member 202.

The reason why the bond strength between the substrate member 201 andthe optical member 202 of the optical element 4 is enhanced will bebriefly described below. As disclosed in Japanese Patent ApplicationLaid-Open Gazette No. Hei 9-221342 (JP 9-221342 A), surface roughness ofa composition surface is known as a factor that affects the bondstrength in the optical contact. However, it is recently known that achemical factor also has an influence in addition to the surfaceroughness in the case of the optical contact. The inventor of thepresent invention has found out that it is possible to enhance thebonding strength between the substrate member 201 and the optical member202, which collectively constitute the optical element 4 at the tip ofthe projection optical system PL, by controlling such a chemical factor.

In the conventional optical contact among oxide optical materials,hydroxyl groups (—OH) exist in high density on both of the surfaces usedfor bonding. Accordingly, it is conceivable that covalent bondingattributable to hydrogen bonding or dehydrative condensation occurs whenclosely attaching these surfaces to each other, which brings about firmbond. Meanwhile, in terms of the optical element 4 of this embodiment, asurface of a fluoride (CaF₂, specifically) constituting the substratemember 201 of the optical element 4 has low density of hydroxyl groupsas compared to a surface of an oxide. Therefore, it is conceivable thatit is difficult to obtain firm bond even when the fluoride is closelyattached to the optical member 202 without any treatment. Accordingly, asufficient amount of hydroxyl groups are introduced to the compositionsurface by coating the fluoride surface of the substrate member 201 withthe coating film 203 made of an oxide. In this way, it is possible toachieve firm optical contact between the substrate member 201 and theoptical member 202. To be more precise, the thin coating film 203 madeof silicon dioxide (SiO₂) is uniformly deposited on the substrate member201 by use of the vacuum vapor deposition method.

Moreover, since the coating film 203 made of silicon dioxide is formedon the substrate member 201 made of calcium fluoride by use of thevacuum vapor deposition method, it is possible to suppress theoccurrence of cracks or the like on the coating film 203. That is, thereis not a large difference between the thermal expansion coefficient ofcalcium fluoride and the thermal expansion coefficient of silicondioxide. Accordingly, it is possible to prevent occurrence of cracks orpersistence of pressure distortion on the coating film 203 when thecoating film 203 is formed on the heated substrate member 201 and thenthese constituents are cooled down to a room temperature. Incidentally,when a fluoride film is formed on silica, cracks are likely to occur onthe film because there is a large difference in the thermal expansioncoefficient (approximately one order of difference) therebetween.

FIG. 26 to FIG. 29 are views for briefly explaining a manufacturingprocess for the optical element 4 shown in FIG. 25. Firstly, as shown inFIG. 26, the substrate member 201 being the optical element having agiven optical surface OS1 is prepared by processing calcium fluoride(CaF₂). Then, as shown in FIG. 27, a SiO₂ layer is deposited on theoptical surface OS1 while heating the substrate member 201, therebyforming the coating film 203. In this way, it is possible to prepare thesubstrate member 201 having the coating film 203. In this case, it ispossible to form the high-density coating film 203 having a high degreeof adhesion to the substrate member 201 by use of the vacuum vapordeposition method. Next, as shown in FIG. 28, the optical member 202having a given optical surface OS2 is prepared by processing syntheticsilica (SiO₂). Lastly, as shown in FIG. 29, the substrate member 201 andthe optical member 202 are attached to each other to form the opticalcontact between a surface OS3 of the coating film 203 on the substratemember 203 and the optical surface OS2 of the optical member 202. Theoptical element 4 is finished accordingly.

In a concrete example of fabrication, the optical surface OS1 on theoutgoing side of calcium fluoride (CaF₂) constituting the substratemember 201 of the optical element 4 is formed into a planar surface.Further, the substrate material 201 is heated at the time of filmformation by vacuum deposition, and the coating film 203 is formed in afilm thickness of about 10 nm. Meanwhile, in terms of the optical member202, a synthetic silica substrate is formed into a parallel plate havinga thickness of 1 mm. Thereafter, an optical contact surface of thesubstrate member 201 and an optical contact surface of the opticalmember 202 of the optical element 4 are attached and joined to eachother without using an adhesive. Then, an experiment described below iscarried out to confirm strength of the optical contact of the opticalelement 4 thus formed.

Specifically, optical transmittance (%) at the wavelength of 193.4 nm ismeasured with an ultraviolet spectrophotometer to evaluate the opticaltransmittance of the optical element 4. Moreover, a tension load test iscarried out by use of a high-precision universal material testingmachine in order to evaluate the strength of the optical element 4.Here, in the tension load test, a tension load is applied in thedirection of tearing the optical member 202 off the substrate member 201of the optical element 4, or in other words, a tension load in theperpendicular direction to the optical contact surfaces. The value ofthe load consumed to detach the optical member 202 is defined as adetachment load (Kgf/cm²). For the purpose of comparison, anothersubstrate member 201 without the coating film 203 is prepared and acomparative sample is formed by subjecting this substrate member 201 andthe optical member 202 directly to the optical contact. Results are showin Table 9 below.

TABLE 9 Detachment load Transmittance (%) (Kgf/cm²) Example (with SiO₂layer) 91.5 31.8 Comparative Example 91.5 10.3 (without SiO₂ layer)

As it is apparent in Table 9 shown above, the optical element 4 of thisembodiment (Example: with the SiO₂ layer) has several times as largeanti-detachment strength as the optical element of the comparativesample (Comparative Example: without the SiO₂ layer) concerning theoptical contact. It is also apparent that a loss in light intensityconcerning the exposure light wavelength is almost equal between theseoptical elements.

Back to FIG. 1, the liquid circulation device includes a liquid supplydevice 5 and a liquid recovery device 6. Of these devices, the liquidsupply device 5 includes a tank for the liquid 7, a booster pump (notshown), a temperature control device, and the like. The liquid supplydevice 5 supplies the temperature-controlled liquid 7 into a spacebetween the wafer W and the tip portion of the optical element 4 througha supply tube 21 and an exhaust nozzle 21 a. Meanwhile, the liquidrecovery device 6 includes a tank for the liquid 7, a suction pump, andthe like. The liquid recovery device 6 recovers the liquid 7 in thespace between the wafer W and the tip portion of the optical element 4through a recovery tube 23 and intake nozzles 23 a and 23 b. Thetemperature of the liquid 7 circulated by the liquid circulation deviceis set to substantially the same degree as the temperature inside achamber in which the projection exposure apparatus of this embodiment ishoused, for example. Here, the refractive index of pure water n relativeto an exposure light beam having a wavelength around 200 nm isapproximately equal to 1.44, and the ArF excimer laser beam having thewavelength of 193 nm is therefore reduced by 1/n times on the wafer W oris virtually reduced to 134 nm. In this way, it is possible to achievehigh resolution.

FIG. 3 is a plan view showing positional relations concerning the Xdirection among the exhaust nozzle 21 a and the intake nozzles 23 a and23 b of FIG. 1, and FIG. 4 is a plan view showing positional relationsconcerning the Y direction among the exhaust nozzle 21 a and the intakenozzles 23 a and 23 b of FIG. 1.

As shown in FIG. 3, a first exhaust nozzle 21 a having an elongated tipportion is disposed in the +X direction so as to sandwich a tip portion4A of the optical element 4 which is an object lens of spotlight of theprojection optical system, and a second exhaust nozzle 22 a having anelongated tip portion is disposed in the −X direction. These first andsecond exhaust nozzles 21 a and 22 a are connected to the liquid supplydevice 5 through first and second supply tubes 21 and 22, respectively.Meanwhile, a pair of first intake nozzles 23 a having spread tipportions are disposed in the +X direction so as to sandwich the tipportion 4A of the optical element 4, and a pair of second intake nozzle24 a having spread tip portions are disposed in the −X direction. Thesefirst and second intake nozzles 23 a and 24 a are connected to theliquid recovery device 6 through first and second recovery tubes 23 and24, respectively.

When the wafer W is moved stepwise in a direction (the −X direction) ofan arrow 25A indicated with a solid line, the liquid 7 is supplied tothe space between the tip portion 4A of the optical element 4 and thewafer W through the first supply tube 21 and the first exhaust nozzle 21a. At the same time, the liquid 7 supplied to the space between the tipportion 4A of the optical element 4 and the wafer W is recovered throughthe second recovery tube 24 and the second intake nozzles 24 a. On theother hand, when the wafer W is moved stepwise in a direction (the +Xdirection) of an arrow 26A indicated with a dot line, the liquid 7 issupplied to the space between the tip portion 4A of the optical element4 and the wafer W through the second supply tube 22 and the secondexhaust nozzle 22 a. At the same time, the liquid 7 supplied to thespace between the tip portion 4A of the optical element 4 and the waferW is recovered through the first recovery tube 23 and the first intakenozzles 23 a.

As shown in FIG. 4, a third exhaust nozzle 27 a having an elongated tipportion is disposed in the +Y direction so as to sandwich the tipportion 4A of the optical element 4, and a fourth exhaust nozzle 28 ahaving an elongated tip portion is disposed in the −Y direction. Thesethird and fourth exhaust nozzles 27 a and 28 a are connected to theliquid supply device 5 through third and fourth supply tubes 27 and 28,respectively. Meanwhile, a pair of third intake nozzles 29 a havingspread tip portions are disposed in the +Y direction so as to sandwichthe tip portion 4A of the optical element 4, and a pair of fourth intakenozzle 30 a having spread tip portions are disposed in the −Y direction.These third and fourth intake nozzles 29 a and 30 a are connected to theliquid recovery device 6 through third and fourth recovery tubes 29 and30, respectively.

When the wafer W is moved stepwise in the ±Y directions, it is similarto the above-described stepwise movement in the ±X directions.Specifically, the liquid 7 is discharged from the corresponding nozzleout of the third and fourth nozzles 27 a and 28 a by switching the thirdand fourth supply tubes 27 and 28. At the same time, the liquid 7 isaspirated through the corresponding pair of nozzles out of the third andfourth intake nozzles 29 a and 30 a by switching the third and fourthrecovery tubes 29 and 30.

Here, in addition to the nozzles 23 a to 30 a configured to supply andrecover the liquid 7 along the X direction and the Y direction asdescribed above, it is also possible to provide nozzles for supplyingand recovering the liquid 7 along oblique directions, for example.

Back to FIG. 1, the main control system 14 adjusts positions and postureof the reticle R by transmitting a control signal to the drive mechanismincorporated in the reticle stage device RST and thereby finely movingthe reticle stage. At this time, the positions in terms of the Xdirection, the Y direction, and the direction of rotation of the reticleR are measured with the unillustrated reticle laser interferometer.

Moreover, the main control system 14 adjusts a focal position and a tiltangle of the wafer W by transmitting a control signal to the wafer stagedrive mechanism 15 and finely moving the Z stage 9 through the waferstage drive system 15. Meanwhile, the main control system 14 adjusts thepositions in terms of the X direction, the Y direction, and thedirection of rotation of the wafer W by transmitting a control signal tothe wafer stage drive mechanism 15 and finely moving the XY stage 10through the wafer stage drive system 15. At this time, the positions interms of the X direction, the Y direction, and the direction of rotationof the wafer W are measured with the wafer laser interferometer 13.

At the time of exposure, the main control system 14 sequentially movesrespective shot regions on the wafer W stepwise to a position ofexposure by transmitting a control signal to the wafer stage drivesystem 15 and driving the XY stage 10 with the wafer stage drive system15. Specifically, an operation for exposing the pattern image of thereticle R onto the wafer W is repeated in accordance with the step andrepeat method.

In the course of the exposure as well as before and after the exposure,the main control system 14 appropriately operates the liquid circulationdevice including the liquid supply device 5 and the liquid recoverydevice 6, thereby controlling an amount of supply and an amount ofrecovery of the liquid 7 to fill the space between a lower end of theprojection optical system PL and the wafer W in the course of movementof the wafer W. As shown in FIG. 5, when the wafer W is traveling in the−X direction along the arrow 25A, for example, the liquid 7 suppliedfrom the first exhaust nozzle 21 a flows in the direction (the −Xdirection) of an arrow 25A and is recovered by the second intake nozzles23 a and 23 b. In order to maintain a constant amount of the liquid 7 tofill the space between the optical element 4 and the wafer W in thecourse of movement of the wafer W, an amount of supply Vi (m³/s) and anamount of recovery Vo (m³/s) of the liquid 7 are set equal. Moreover, inorder to avoid excessive or insufficient circulation of the liquid 7, atotal amount of the amount of supply Vi and the amount of recovery Vo ofthe liquid 7 is adjusted based on a traveling speed v of the XY stage10, i.e. the wafer W. For example, the amount of supply Vi and theamount of recovery Vo of the liquid 7 are calculated by the followingformula 1.

Vi=Vo=D·v·d  (1)

Here, D denotes a diameter (m) of the tip portion 4A of the opticalelement 4. Meanwhile, v denotes the traveling speed (m/s) of the wafer Won the XY stage 10 and d denotes a working distance (m) of theprojection optical system PL. The main control system 14 controls thestepwise movement of the XY stage 10, and is able to fill the liquid 7in the space between the optical element 4 and the wafer W constantly inthe stable state by calculating the amount of supply Vi and the amountof recovery Vo of the liquid 7 based on the formula 1 corresponding tothe stepwise movement of the XY stage 10. By controlling amount ofsupply Vi and the amount of recovery Vo of the liquid 7 as describedabove, it is possible to prevent the liquid 7 from leaking out of theoptical element and to prevent the optical member 202 at the tip of theoptical element 4 from being soaked in the liquid 7. Accordingly, it ispossible to prevent corrosion of the optical element 4 and damage on theoptical contact with the optical member 202, and thereby to maintain theperformance of the optical element 4 over a long period of time. Inother words, it is possible to reduce the frequency of replacement ofthe optical element 4 and to maintain high throughput in the exposureprocess on the wafer W. Eventually, it is possible to efficientlymanufacture end products in high quality.

The foregoing explanation relates to the case of moving the wafer W inthe ±X directions. It is also possible to maintain the amount of theliquid 7 between the optical element 4 and the wafer W stably byperforming similar control in the case of moving the wafer W in the ±Ydirections as well.

Here, it is preferable to adjust the working distance d of theprojection optical system PL as narrow as possible in order to retainthe liquid 7 stably between the optical element 4 and the wafer W. Theworking distance d of the projection optical system PL is set to about 2mm, for example.

As it is apparent from the above description, the projection exposureapparatus of this embodiment applies the projection optical system PLincorporating the optical element 4 having high optical transmittance,which system is obtained by firmly joining the optical element 4 to theoptical member 202 by the excellent optical contact. In this way, it ispossible to perform the exposure process of the liquid immersion typewhich can maintain the high performance over a long period of time.

Although the present invention has been described in terms of Embodiment16, it is to be noted that the present invention is not limited only tothis Embodiment 16. For example, as for the material of the substratemember 201 of the optical element 4, it is possible to use bariumfluoride (BaF₂), magnesium fluoride (MgF₂), and the like instead ofcalcium fluoride depending on the wavelength used therein.

Meanwhile, as for the material of the coating film 203 of the opticalelement 4, it is possible to use aluminum oxide (Al₂O₃) and the likeinstead of silicon dioxide (SiO₂) depending on the wavelength usedtherein. Here, the coating film 203 is not limited to a single-layerfilm and it is also possible to form the coating film 203 by depositingtwo or more different types of films. Nevertheless, it is possible toform an oxide film such as silicon dioxide as the outermost layer.

Meanwhile, as for the material of the optical member 202, it is possibleto use sapphire instead of silica depending on the wavelength usedtherein. In addition, the optical member 202 may be formed by depositinga thin film of silicon dioxide (SiO₂) or the like on a surface offluoride glass or the like.

Meanwhile, the shapes of the substrate member 201 and the optical member202 of the optical element 4 are not limited those described in thisembodiment. For example, the surfaces of the substrate member 201 andthe optical member 202 are not limited to flat surfaces, and it ispossible to apply various curved surfaces having a variety of curvature.

Moreover, in this embodiment, the silicon dioxide (SiO₂) film is formedon the substrate member 201 by use of the vacuum vapor depositionmethod. Instead, it is possible to use other film forming methodsincluding the ion beam assisted vapor deposition method, the gas clusterion beam assisted vapor deposition method, the ion plating method, theion beam sputtering method, the magnetron sputtering method, the biassputtering method, the ECR sputtering method, the RF sputtering method,the thermal CVD method, the plasma enhanced CVD method, and the photoCVD method.

Further, the clearance between the tip portion 4A of the optical element4 and the surface of the wafer W is entirely filled with the liquid 7 inthis embodiment. Instead, it is also possible to interpose the liquidpartially in this clearance.

Although pure water is used as the liquid 7 in this embodiment, theliquid is not limited only to the pure water. It is also possible to usevarious other liquids (such as cedar oil), which allow transmission ofthe exposure light beam and remain stable against the photoresist withwhich the projection optical system and the surface of the wafer werecoated. Here, when a F₂ laser beam is used as the exposure light beam,it is possible to use a fluorinated liquid that allows transmission ofthe F₂ laser beam as the liquid 7. Such a fluorinated liquid may befluorinated oil or perfluoropolyether (PFPE), for example.

Moreover, the layout and the number of the nozzles and the like in thisembodiment are shown merely as an example. It is therefore possible tochange the layout and the number of the nozzles as appropriate so as tocorrespond to the size, the traveling speed, and other factors of thewafer W.

Embodiment 17

Next, a projection exposure apparatus of Embodiment 17 will be describedwith reference to the accompanying drawings. FIG. 30 is a front viewshowing a lower part of a projection optical system PLA, the liquidsupply device 5, the liquid recovery device 6, and the like of theprojection exposure apparatus applying the step-and-scan methodaccording to Embodiment 17. It is to be noted that an XYZ orthogonalcoordinate system as illustrated in FIG. 1 will be set up in thefollowing explanation, and positional relations of respective memberswill be described with reference to this XYZ orthogonal coordinatesystem. In terms of the XYZ orthogonal coordinate system, an X axis anda Y axis are set parallel to a wafer W while a Z axis is set in theorthogonal direction to the wafer W. In the XYZ orthogonal coordinatesystem in the drawing, an XY plane is actually set to a parallel planeto a horizontal plane while the Z axis is set in the vertical direction.Moreover, in the description concerning FIG. 30, constituents of thisembodiment which are identical to those in the projection exposureapparatus of Embodiment 1 are designated by the same reference numerals.

In this projection exposure apparatus, a transmissive optical element 32at the bottom end of a lens barrel 3A of the projection optical systemPLA includes a tip portion 32A, which is reduced into a rectangle havinga longitudinal edge in the Y direction (a non-scanning direction) whileleaving only a necessary part for scanning exposure. At the time ofscanning exposure, part of a pattern image of a reticle (not shown) isprojected on a rectangular exposure region immediately below the tipportion 32A on the wafer W side. When the reticle (not shown) travels inthe −X direction (or in the +X direction) at a speed V, the wafer Wtravels in the +X direction (or in the −X direction) by use of the XYstage 10 at a speed of β·V (β denotes the projection magnitude)synchronously, with respect to the projection optical system PLA. Then,after completing exposure on one shot region, the next shot region movesto a scanning start position by moving the wafer W stepwise. Thereafter,the respective shot regions are sequentially subjected to exposure inaccordance with the step-and-scan method.

This embodiment applies the transmissive optical element 32 which issimilar to the transmissive element 4 (see FIG. 2) used in Embodiment 1.Specifically, the base material of the transmissive optical element 32is made of calcium fluoride, and crystal orientation of the film formingsurface of the calcium fluoride element is defined as the (111) plane.Moreover, the magnesium fluoride (MgF₂) film F1 and the silicon dioxide(SiO₂) film F2 collectively serving as the anti-dissolution film areformed at the tip portion 32A on the wafer W side of the transmissiveoptical element 32, or the portion where the exposure light passesthrough, by use of the vacuum vapor deposition method. In addition, thesilicon dioxide (SiO₂) film F3 is formed thereon by use of the wet filmforming method.

Meanwhile, the tantalum (Ta) film F5 (F4) serving as the metalanti-dissolution film (which also functions as the adhesion reinforcingfilm) is formed on a tapered surface 32B of the transmissive opticalelement 32, or a portion where the exposure light does not pass through,by use of the sputtering method. In addition, the silicon dioxide (SiO₂)film F6 serving as the protective film for the metal anti-dissolutionfilm (the protective film for the anti-dissolution film) for protectingthe metal anti-dissolution film is formed on the surface of the metalanti-dissolution film (the anti-dissolution film) F5 by the wet filmforming method simultaneously with formation of the silicon dioxide(SiO₂) film F3. Here, the metal anti-dissolution film (theanti-dissolution film) F5 to be formed on the tapered surface 32B of thetransmissive optical element 32 has solubility to pure water equal to orbelow 2 ppt and packing density equal to or above 95%. Moreover, meanreflectance of the anti-dissolution films F1 to F3 formed on the tipportion 32A of the transmissive optical element 32 is equal to or below2% when an exit angle of the exposure light beam is set to 50 degrees.

The liquid immersion method is also applied to this Embodiment 17 assimilar to Embodiment 1. Accordingly, a liquid 7 fills the space betweenthe transmissive optical element 32 and the surface of the wafer W inthe course of scanning exposure. Pure water is used as the liquid 7.Moreover, supply and recovery of the liquid 7 are performed by use ofthe liquid supply device 5 and the liquid recovery device 6,respectively.

FIG. 31 is a view showing positional relations among the surface (thetip portion 32A and the tapered surface 32B on the wafer W side) of thetransmissive optical element 32 in the projection optical system PLA,and exhaust nozzles as well as intake nozzles configured to supply andrecover the liquid 7 in the X direction. As shown in FIG. 31, threeexhaust nozzles 21 a to 21 c located on the +X side of the tip portion32A and the tapered surface 32B, which have the elongated rectangularshapes in the Y direction, are connected to the liquid supply device 5through the supply tube 21. Moreover, three exhaust nozzles 22 a to 22 clocated on the −X side of the tip portion 32A and the tapered surface32B are connected to the liquid supply device 5 through the supply tube22. Meanwhile, as shown in FIG. 31, two intake nozzles 23 a and 23 blocated on the −X side of the tip portion 32A and the tapered surface32B are connected to the liquid recovery device 6 through the recoverytube 23, and two intake nozzles 24 a and 24 b located on the +X side ofthe tip portion 32A and the tapered surface 32B are connected to theliquid recovery device 6 through the recovery tube 24.

When the wafer W is moved in a scanning direction (the −X direction) ofan arrow indicated with a solid line for performing the scanningexposure, the liquid supply device 5 supplies the liquid 7 to the spacebetween the tip portion 32A as well as the tapered surface 32B of thetransmissive optical element 32 and the wafer W through the supply tube21 and the exhaust nozzles 21 a to 21 c. The liquid recovery device 6recovers the liquid 7, which is supplied from the liquid supply device 5to the space between the tip portion 32A as well as the tapered surface32B and the wafer W, through the recovery tube 23 and the intake nozzles23 a and 23 b. In this case, the liquid 7 flows on the wafer W in the −Xdirection, whereby the space between the transmissive optical element 32and the wafer W is filled with the liquid 7.

On the other hand, when the wafer W is moved in a direction (the +Xdirection) of an arrow indicated with a chain double-dashed line forperforming the scanning exposure, the liquid supply device 5 suppliesthe liquid 7 to the space between the tip portion 32A of thetransmissive optical element 32 and the wafer W through the supply tube22 and the exhaust nozzles 22 a to 22 c. The liquid recovery device 6recovers the liquid 7, which is supplied from the liquid supply device 5to the space between the tip portion 32A and the wafer W, through therecovery tube 24 and the intake nozzles 24 a and 24 b. In this case, theliquid 7 flows on the wafer W in the +X direction, whereby the spacebetween the transmissive optical element 32 and the wafer W is filledwith the liquid 7.

In the meantime, the amount of supply Vi (m³/s) and the amount ofrecovery Vo (m³/s) of the liquid 7 are calculated by the followingformula 2.

Vi=Vo=DSY·v·d  (Formula 2)

Here, DSY denotes the length (m) of the tip portion 32A of the opticalelement 32 in the X direction. Since DSY is preset, the liquid 7 alwaysfills the space between the optical element 32 and the wafer W stably inthe course of scanning exposure by calculating and adjusting the amountof supply Vi (m³/s) and the amount of recovery Vo (m³/s) of the liquid 7based on the formula 2.

Meanwhile, when the wafer W is moved stepwise in the Y direction, theliquid 7 is supplied and recovered along the Y direction in accordancewith the same method as that of Embodiment 1.

FIG. 32 is a view showing positional relations among the tip portion 32Aof the transmissive optical element 32 in the projection optical systemPLA, and exhaust nozzles as well as intake nozzles in the Y direction.As shown in FIG. 32, when the wafer W is moved stepwise in thenon-scanning direction (the −Y direction) orthogonal to the scanningdirection, the liquid 7 is supplied and recovered by use of an exhaustnozzle 27 a and intake nozzles 29 a and 29 b which are arranged in the Ydirection. On the other hand, when the wafer W is moved stepwise in the+Y direction, the liquid 7 is supplied and recovered by use of anexhaust nozzle 28 a and intake nozzles 30 a and 30 b which are arrangedin the Y direction. In this case, the amount of supply Vi (m³/s) and theamount of recovery Vo (m³/s) of the liquid 7 are calculated by thefollowing formula 3.

Vi=Vo=DSX·v·d  (Formula 3)

Here, DSX denotes the length (m) of the tip portion 32A of the opticalelement 32 in the Y direction. As similar to Embodiment 1, the liquid 7continuously fills the space between the optical element 32 and thewafer W, even in the course of stepwise movement in the X direction, byadjusting the amount of supply of the liquid 7 in response to thetraveling speed v of the wafer W.

The projection exposure apparatus of this Embodiment 17 exerts similaroperations and effects to that of Embodiment 1.

Specifically, it is possible to prevent dissolution of the opticalelement in the first place because the anti-dissolution film is formedon the surface of the optical element. Therefore, the optical element isprevented from dissolving in the liquid filling the space between thetip portion of the projection optical system and the substrate. As aresult, it is not necessary to replace the optical element frequentlyand it is possible to maintain high throughput of the exposureapparatus. Moreover, it is not necessary to stop operations of theexposure apparatus in order to replace the corroded optical element, andit is thereby possible to manufacture end products efficiently. Inaddition, the optical element does not dissolve in the liquid and it isthereby possible to maintain the optical performance of the projectionoptical system. Hence it is possible to stabilize the quality of themanufactured end products and to continue exposure in the optimalcondition.

Moreover, according to the projection exposure apparatus of thisEmbodiment 17, the metal anti-dissolution film that also functions asthe adhesion reinforcing film is formed on the tapered surface 32B ofthe transmissive optical element 32 on the wafer W side of theprojection optical system PLA. Therefore, it is possible to attach themetal anti-dissolution film closely to the transmissive optical element32. Meanwhile, since the silicon dioxide (SiO₂) film is formed on thesurface of the metal anti-dissolution film, it is possible to preventdamage on the soft metal anti-dissolution film having low abrasionresistance and thereby to protect the metal anti-dissolution film.Therefore, it is possible to prevent infiltration to and corrosion ofthe transmissive optical element 32 by the liquid 7 interposed betweenthe surface of the wafer W and the projection optical system PLA, andthereby to maintain the optical performance of the projection opticalsystem PLA. Moreover, it is possible to maintain the performance of theexposure apparatus because the transmissive optical element 32 does notdissolve in the liquid 7. In addition, it is not necessary to replacethe transmissive optical element 32 frequently. Therefore, it ispossible to maintain high throughput of the projection exposureapparatus.

Embodiments 18 to 31

Projection exposure apparatuses of Embodiments 18 to 31 are configuredas similar to Embodiment 17 except that the transmissive opticalelements 4 used in Embodiments 2 to 15 are respectively applied as thetransmissive optical elements 32.

The projection exposure apparatuses of Embodiments 18 to 31, whichrespectively have the above-described configuration, exert similaroperations and effects to those of Embodiments 2 to 15, respectively.

Embodiment 32

A projection exposure apparatus is configured as similar to Embodiment17 except applying an optical element with which an optical memberoptically contacts through a film as described below. Note that theprojection exposure apparatus of Embodiment 32 is configured to performexposure in accordance with the step-and-scan method by partiallymodifying the projection exposure apparatus of Embodiment 16.Accordingly, constituents common to those in Embodiment 16 will bedesignated by the same reference numerals and duplicate explanationswill be omitted herein.

In the projection exposure apparatus of Embodiment 32 shown in FIG. 30,the transmissive optical element 32, which protrudes from the bottom endof the lens barrel 3A of the projection optical system PLA includes atip portion 32B, is reduced into a rectangle having a longitudinal edgein the Y direction (a non-scanning direction) while leaving only anecessary part for scanning exposure. At the time of scanning exposure,part of a pattern image of a reticle (not shown) is projected on arectangular exposure region immediately below the tip portion 32B. Whenthe reticle (not shown) travels in the −X direction (or in the +Xdirection) at the speed V, the wafer W travels in the +X direction (orin the −X direction) by use of the XY stage 10 at the speed of β·V (βdenotes the projection magnitude) synchronously, with regard to theprojection optical system PLA. Then, after completing exposure on oneshot region, the next shot region moves to a scanning start position bymoving the wafer W stepwise. Thereafter, the respective shot regions aresequentially subjected to exposure in accordance with the step-and-scanmethod.

The liquid immersion method is also applied to this Embodiment 32 assimilar to Embodiment 16. Accordingly, the liquid 7 fills the spacebetween the lower surface of the optical element 32 and the surface ofthe wafer W in the course of scanning exposure. Here, as similar toEmbodiment 16, the optical element 32 includes the substrate member 201made of calcium fluoride and the optical member 202 made of silica (SeeFIG. 25). Moreover, the thin coating film 203 made of silicon dioxide(SiO₂) is uniformly deposited on the substrate member 201 of the opticalelement 32 to achieve firm optical contact. In this way, it is possibleto protect the substrate member 201 made of calcium fluoride against theliquid 7, and thereby to enhance durability of the optical element 32and eventually durability of the projection optical system PLA.

FIG. 31 is a view showing positional relations among exhaust nozzles andintake nozzles configured to supply and recover the liquid to and fromthe space immediately below the projection optical system PLA. Threeexhaust nozzles 21 a to 21 c located on the +X side of the tip portion32A are connected to the liquid supply device 5 through the supply tube21. Moreover, three exhaust nozzles 22 a to 22 c located on the −X sideof the tip portion 32A are connected to the liquid supply device 5through the supply tube 22. Meanwhile, two intake nozzles 23 a and 23 blocated on the −X side of the tip portion 32A are connected to theliquid recovery device 6 through the recovery tube 23, and two intakenozzles 24 a and 24 b located on the +X side of the tip portion 32A areconnected to the liquid recovery device 6 through the recovery tube 24.

When the wafer W is moved in the scanning direction (the −X direction)of the arrow indicated with the solid line for performing the scanningexposure, the liquid supply device 5 supplies the liquid 7 to the spacebetween the tip portion 32A of the optical element 32 and the wafer Wthrough the supply tube 21 and the exhaust nozzles 21 a to 21 c. Theliquid recovery device 6 recovers the liquid 7 retained in the spacebetween the tip portion 32A and the wafer W through the recovery tube 23and the intake nozzles 23 a and 23 b. In this case, the liquid 7 flowson the wafer W in the −X direction, whereby the space between theoptical element 32 and the wafer W is constantly filled with the liquid7.

On the other hand, when the wafer W is moved in the direction (the +Xdirection) of the arrow indicated with the chain double-dashed line forperforming the scanning exposure, the liquid supply device 5 suppliesthe liquid 7 to the space between the tip portion 32A of the opticalelement 32 and the wafer W through the supply tube 22 and the exhaustnozzles 22 a to 22 c. The liquid recovery device 6 recovers the liquid 7retained in the space between the tip portion 32A and the wafer Wthrough the recovery tube 24 and the intake nozzles 24 a and 24 b. Inthis case, the liquid 7 flows on the wafer W in the +X direction,whereby the space between the optical element 32 and the wafer W isconstantly filled with the liquid 7.

Here, the layout and other features of the exhaust nozzles and theintake nozzles, which are used for circulating the liquid 7 in the spacebetween the optical element 32 and the wafer W, when moving the wafer Win the ±Y directions are substantially similar to those in Embodiment16.

The scanning projection exposure apparatus of Embodiment 32 applies theprojection optical system PLA incorporating the optical element 32having high optical transmittance, which system is obtained by firmlyjoining the optical element 32 to the optical member 202 by theexcellent optical contact. In this way, it is possible to perform theexposure process of the liquid immersion type which can maintain thehigh performance over a long period of time.

Embodiment 33

An exposure apparatus according to Embodiment 33 will be described withreference to the accompanying drawings. The exposure apparatus of thisembodiment is a liquid immersion type exposure apparatus adopting theliquid immersion method in order to improve resolution and to virtuallywiden a depth of focus by virtually shortening an exposure wavelength.FIG. 33 is a view showing a first optical element LS1 located closest toan image plane of a projection optical system PL, a second opticalelement LS2 located second closest to the imaging surface of theprojection optical system PL after the first optical element LS1, andthe like out of multiple optical elements made of calcium fluoride whichcollectively constitute the projection optical system PL of the exposureapparatus of this embodiment.

This exposure apparatus includes a first liquid immersion mechanism forfilling a space between a lower surface T1 of the first optical elementLS1, which is the closest optical element to the image plane of theprojection optical system PL among the multiple optical elementsconstituting the projection optical system PL, and a substrate P with afirst liquid LQ1. The substrate P is provided on the image plane side ofthe projection optical system PL, and the lower surface T1 of the firstoptical element LS1 is disposed opposite to a surface of the substrateP. The first liquid immersion mechanism includes a first liquid supplymechanism 90 for supplying the first liquid LQ1 to the space between thelower surface T1 of the first optical element LS1 and the substrate P,and a first liquid recovery mechanism 91 for recovering the first liquidLQ1 supplied from the first liquid supply mechanism 90.

Moreover, this exposure apparatus includes a second liquid immersionmechanism for filling a space between the first optical element LS1 andthe second optical element LS2, which is the second closest opticalelement to the image plane of the projection optical system PL, with asecond liquid LQ2. The second optical element LS2 is disposed above thefirst optical element LS1. The upper surface T2 of the first opticalelement LS1 is disposed opposite to the lower surface T3 of the secondoptical element LS2. The second liquid immersion mechanism includes asecond liquid supply mechanism 92 for supplying the second liquid LQ2 tothe space between the first optical element LS1 and the second opticalelement LS2, and a second liquid recovery mechanism 93 for recoveringthe second liquid LQ2 supplied from the second liquid supply mechanism92.

A lens barrel PK includes a counter surface 89 which faces a peripheralregion of the upper surface T2 of the first optical element LS1.Moreover, a first sealing member 94 is provided between the peripheralregion of the upper surface T2 and the counter surface 89. The firstsealing member 94 is formed of an O-ring (such as “Kalrez” made byDuPont-Dow) or a C-ring, for example. The first sealing member 94prevents leakage of the second liquid LQ2 located on the upper surfaceT2 to the outside of the upper surface T2, or to the outside of the lensbarrel PK. Meanwhile, a second sealing member 95 is provided between aside surface C2 of the second optical element LS2 and an inner sidesurface PKC of the lens barrel PK. The second sealing member 95 isformed of a V-ring, for example. The second sealing member 95 regulatescirculation of the second liquid LQ2, damp gas derived from the secondliquid LQ2, and the like to an upper part of the second optical elementLS2 inside the lens barrel PK.

Moreover, a third sealing member 96 is provided between a side surfaceC1 of the first optical element LS1 and the inner side surface PKC ofthe lens barrel PK. The third sealing member 96 is formed of a V-ring,for example. The third sealing member 96 regulates circulation of thefirst liquid LQ1, damp gas derived from the first liquid LQ1, and thelike to an upper part of the first optical element LS1 inside the lensbarrel PK.

A light-shielding film made of gold (Au) is formed in a thickness of 150nm on each of the side surface (a tapered surface) C1 of the firstoptical element LS1 and the side surface (a tapered surface) C2 of thesecond optical element LS2. Therefore, by using these light-shieldingfilms, it is possible to prevent irradiation of the exposure light beamand reflection of the exposure light beam by the wafer onto the firstsealing member 94, the second sealing member 95, and the third sealingmember 96 which are provided in the periphery of the tapered surfaces ofthe transmissive optical element on the substrate's side of theprojection optical system. In this way, it is possible to preventdeterioration of the sealing members.

In the above-described Embodiment 33, the light-shielding film which isthe metal film made of gold (Au) is formed on each of the side surface(the tapered surface) C1 of the first optical element LS1 and the sidesurface (the tapered surface) C2 of the second optical element LS2.Instead, the light-shielding film formed as the metal film may be formedof at least one of gold (Au), platinum (Pt), silver (Ag), nickel (Ni),tantalum (Ta), tungsten (W), palladium (Pd), molybdenum (Mo), titanium(Ti), and chromium (Cr). Alternatively, it is also possible to form thelight-shielding film as a metal oxide film. In this case, the metaloxide film may be formed of at least one of zirconium dioxide (ZrO₂),hafnium dioxide (HfO₂), titanium dioxide (TiO₂), tantalum pentoxide(Ta₂O₅), silicon monoxide (SiO), and chromium oxide (Cr₂O₃).

The above-described Embodiments 1 to 33 apply the exposure apparatusconfigured to fill the space between the projection optical system PLand the substrate P locally with the liquid. However, the presentinvention is also applicable to a liquid immersion exposure apparatusdisclosed in Japanese Patent Application Laid-Open Gazette No. Hei6-124873 (JP 6-124873 A), which apparatus is configured to move a stagethat retains a substrate subject to exposure in a liquid tank, or to aliquid immersion exposure apparatus disclosed in Japanese PatentApplication Laid-Open Gazette No. Hei 10-303114 (JP 10-303114 A), whichapparatus is configured to have a liquid tank having a predetermineddepth, the tank being formed on a stage, and to retain a substrateinside the tank.

Moreover, the present invention is also applicable to a twin-stage typeexposure apparatus including two stages configured to locate processtarget substrates such as wafers individually and to move the substratesindependently in XY directions. Such a twin-stage type exposureapparatus is disclosed in Japanese Patent Application Laid-Open GazetteNo. Hei 10-163099 (JP 10-163099 A), Japanese Patent ApplicationLaid-Open Gazette No. Hei 10-214783 (JP 10-214783 A), InternationalApplication National-Phase Publication No. 2000-505958 (JP 2000-505958A), and the like.

In addition to the above explanations, other configurations applicableto the exposure apparatus of the present invention are disclosed inInternational Publication No. WO2004/019128 (WO 2004-019128 A),International Publication No. WO2004/053950 (WO 2004-053950 A), andInternational Publication No. WO2004/053951 (WO 2004-053951 A); theentire contents of which are incorporated herein by reference.

EXAMPLES

The present invention will be described more in detail below based onexamples and comparative examples. It is to be noted, however, that thepresent invention will not be limited only to the following examples.

Example 1

FIG. 34 is a view showing a configuration of an optical element 50 ofthe present invention. As shown in FIG. 34, the optical element 50 wasformed by depositing silicon oxide 54 in an optical film thickness of0.55λ (λ=193 nm) on a substrate of calcium fluoride 52, of which acrystal orientation of a film forming surface 52 a is defined as a (111)plane, as an anti-dissolution film for the calcium fluoride 52 by use ofthe RF sputtering method. Here, as shown in FIG. 35, the optical filmthickness of the silicon oxide film must be restricted so as to suppressa ghost phenomenon caused by residual reflection of light on a surfaceof the substrate of the calcium fluoride 52 when the light is incidenton the calcium fluoride 52 along the direction of an arrow 56 indicatedwith a solid line and is reflected by the calcium fluoride 52 along thedirection of an arrow 58 indicated with a dashed line. Specifically,FIG. 36 is a graph showing residual reflectivity of the calcium fluoridewhen the light is incident on the calcium fluoride substrate. Theresidual reflectivity of the calcium fluoride in the case of not formingthe silicon oxide film on the calcium fluoride substrate is indicatedwith a solid line 60 in FIG. 36. Meanwhile, the residual reflectivity ofthe calcium fluoride in the case of forming the silicon oxide film onthe calcium fluoride substrate is indicated with a dashed line 62 inFIG. 36. As shown in FIG. 36, the optical film thickness of the siliconoxide film is set such that the residual reflectivity of the calciumfluoride becomes equal to or below 0.5% when an incident angle of thelight incident on the calcium fluoride is equal to 60 degrees.

An experiment was performed by use of the optical element 50. FIG. 37 isa view showing a configuration of an experimental device used in thisexample. Pure water 66 at the temperature of 70° C. is put into a tank64 made of polyether ether ketone (PEEK) which is large enough for thevolume of the optical element 50. A beater 68 made of Teflon (registeredtrademark) is put into the pure water 66. As shown in FIG. 37, theoptical element 50 is put into the pure water 66 so that only the halfof the optical element 50 is soaked in the pure water 66. The tank 64containing the optical element 50, the pure water 66, and the beater 68is put into a constant-temperature tank 70 to maintain a constanttemperature.

The tank 64 used herein has a sufficiently large size relative to thevolume of the optical element 50 to reduce a liquid level changeattributable to evaporation of the pure water 66. Moreover, the beater68 is used for maintaining constant solubility even when the opticalelement 50 dissolves in the pure water 66 and thereby generates a buffersolution. After a lapse of 3 hours while the optical element 50 wassoaked in the pure water 66, a step between the portion of the opticalelement 50 not soaked in the pure water 66 and the portion of theoptical element 50 soaked in the pure water 66 was measured with astep-measurement gauge having resolving power of 0.5 nm. No step wasobserved.

Example 2

FIG. 38 is a view showing a configuration of an optical element 74 ofthe present invention. As shown in FIG. 38, the optical element 74 wasformed by depositing lanthanum fluoride 78 in an optical film thicknessof 0.68λ (λ=193 nm) on a substrate of calcium fluoride 76, of which acrystal orientation of a film forming surface 76 a is defined as a (111)plane, as an anti-dissolution film for the calcium fluoride 76 by use ofthe vacuum vapor deposition method. It has been known that the lanthanumfluoride 78 on the (111) plane of the calcium fluoride 76 reflects thecrystal orientation of the calcium fluoride 76 and therebyheteroepitaxially grows on the (111) plane (see WO 03/009015).Therefore, the deposited lanthanum fluoride 78 forms a very densecrystal structure with very few defects.

An experiment was performed by use of the optical element 74. Theconfiguration of an experimental device used in this example is the sameas the configuration of the experimental device used in Example 1 shownin FIG. 37. Accordingly, the same constituents will be designated by thesame reference numerals used in Example 1, in the following description.

First, the pure water 66 at the temperature of 70° C. is put into thetank 64 which is large enough for the volume of the optical element 74,and a beater 68 is put into pure water 66. The optical element 74 is putinto the pure water 66 so that only the half of the optical element 74is soaked in the pure water 66. The tank 64 containing the opticalelement 74, the pure water 66, and the beater 68 was put into theconstant-temperature tank 70 to maintain a constant temperature. After alapse of 3 hours while the optical element 74 was soaked in the purewater 66, a step between the portion of the optical element 74 notsoaked in the pure water 66 and the portion of the optical element 74soaked in the pure water 66 is measured with the step-measurement gaugehaving the resolving power of 0.5 nm. No step was observed.

In this example, the vacuum vapor deposition method was used as the filmforming method for the anti-dissolution film in order to form theanti-dissolution film having the dense structure. However, it is alsopossible to form the anti-dissolution film by use of the sputteringmethod or the CVD method.

Comparative Example 1

An experiment was performed in terms of a calcium fluoride substratewithout an anti-dissolution film. FIG. 39 is a view showing aconfiguration of an experimental device used in this comparativeexample. In this comparative example, a calcium fluoride substrate 72 isused instead of the optical element 50 of Example 1. Other features ofthe experimental device for this comparative example are the same as theconfiguration of the experimental device used in Example 1. Accordingly,the same constituents will be designated by the same reference numeralsin Example 1, in the following description.

First, the pure water 66 at the temperature of 70° C. is put into thetank 64 which is large enough for the volume of the calcium fluoridesubstrate 72, and a beater 68 is put into pure water 66. The calciumfluoride substrate 72 is put into the pure water 66 so that only thehalf of the calcium fluoride substrate 72 is soaked in the pure water66. The tank 64 containing the calcium fluoride substrate 72, the purewater 66, and the beater 68 is put into the constant-temperature tank 70to maintain a constant temperature. After a lapse of 3 hours whilesoaking the calcium fluoride substrate 72 in the pure water 66, a stepbetween the portion of the calcium fluoride substrate 72 not soaked inthe pure water 66 and the portion of the calcium fluoride substrate 72soaked in the pure water 66 was measured with the step-measurement gaugehaving the resolving power of 0.5 nm. A step of 50 nm was observed dueto dissolution of the portion of the calcium fluoride substrate 72soaked in the pure water 66.

According to the optical elements of Example 1 and Example 2, it ispossible to reduce the solubility to pure water at least 1/50 times assmall as that of the optical element of Comparative Example 1. FIG. 40is a graph showing results of measurement of steps measured after theexperiments of the optical elements of Comparative Example 1, Example 1,and Example 2, which are measured with the step-measurement gauge. Asshown in FIG. 40, the calcium fluoride including the anti-dissolutionfilm made of the silicon oxide or the lanthanum fluoride does notdissolve in the pure water. Accordingly, no step is generated.Therefore, it is possible to maintain a transmission wavefront of theprojection optical system in the projection exposure apparatus when thisoptical element is embedded in the liquid contact portion of theprojection exposure apparatus applying the liquid immersion method.

Example 3

FIG. 41 is a view showing a configuration of a transmissive opticalelement 50 of the Example 3. As shown in FIG. 41, an adhesionreinforcing film 53 is formed by depositing tantalum (Ta) in a thicknessof 10 nm on a substrate of calcium fluoride 52 by use of the sputteringmethod. The adhesion reinforcing film 53 has a function to improveadhesion between the calcium fluoride 52 and a metal film 54 to beformed on a surface of the adhesion reinforcing layer 53. Here, the filmthickness required for increasing adhesion is equal to or above 10 nm.However, an effect of adhesion can be achieved by the film thickness ina range from 3 to 5 nm.

Next, the metal film 54 made of gold (Au), which film functions as theanti-dissolution film for preventing dissolution in water, is formed ina thickness of 200 nm on the surface of the adhesion reinforcing film 53by use of the sputtering method.

Here, density of the metal film 54 can be determined by a critical anglein X-ray diffraction. When the film is formed by the sputtering method,packing density of the metal film 54 is equal to or above 97%.Meanwhile, solubility of the metal film 54 to water is equal to or below1 ppt when the film is formed by the sputtering method.

Next, a silicon dioxide (SiO₂) film 55, which functions as theprotective film for the anti-dissolution film for improving mechanicalstrength of the metal film 54, is formed in a thickness of 50 nm on thesurface of the metal film 54 by use of the sputtering method.

An experiment was performed by use of the transmissive optical element50. FIG. 42 is a view showing a configuration of a tester 80 used inthis example. As shown in FIG. 42, the tester 80 includes a sampleholder 81, a circulation pump 82, a deuterated water supply device 83,and a buffer tank 84. One surface of the sample holder 81 is open, andan O-ring 85 is provided on the open surface. The surface of thetransmissive optical element 50 where the adhesion reinforcing film 53,the metal film 54, and the silicon dioxide (SiO₂) film 55 are formed onis attached to the open surface of the sample holder 81 and is sealedwith the O-ring 85. Deuterated water is supplied from the deuteratedwater supply device 83 by use of the circulation pump 82 and is allowedto flow inside the sample holder 81 through the buffer tank 84. Here,the buffer tank 84 is provided in order to prevent transmission ofvibrations of the circulation pump 82 to the sample holder 81. Moreover,by supplying deuterated water (D₂O) instead of pure water (H₂O), it ispossible to measure an amount of deuterated water infiltrating thesurface of the transmissive optical element 50 in the depth directionafter a water resistance test.

A thirty-day water resistance test was conducted by use of the tester 80while setting a traveling speed of deuterated water on the transmissiveoptical element 50 equal to 50 cm/sec. As a result, the films formed onthe surface of the transmissive optical element 50 were not peeled off,and there was no change in the appearance of the transmissive opticalelement 50. Moreover, as a result of evaluation concerning infiltrationof the deuterated water into the surface of the transmissive opticalelement 50 in the depth direction in accordance with the secondary ionmass spectrometry (SIMS), it was confirmed that the deuterated water didnot infiltrate into the metal film 54.

Example 4

FIG. 43 is a view showing a configuration of a transmissive opticalelement 58 of the Example 4. As shown in FIG. 43, a metal film 60 madeof gold (Au), which functions as the anti-dissolution film forpreventing dissolution in water, is formed in a thickness of 200 nm on asurface of a substrate of calcium fluoride 59 by use of the sputteringmethod. Here, density of the metal film 60 can be determined by acritical angle in X-ray diffraction. When the metal film 60 is formed bythe sputtering method, packing density thereof is equal to or above 97%.Meanwhile, solubility of the metal film 60 to water is equal to or below1 ppt when the film is formed by the sputtering method.

Next, a silicon dioxide (SiO₂) film 61, which functions as theprotective film for the anti-dissolution film for improving mechanicalstrength of the metal film 60, is formed in a thickness of 50 nm on thesurface of the metal film 60 by use of the sputtering method.

An experiment was performed by use of the transmissive optical element58. As similar to Example 3, a thirty-day water resistance test wasconducted by use of the tester 80 shown in FIG. 42 while setting atraveling speed of deuterated water on the transmissive optical element58 equal to 50 cm/sec. As a result, the films formed on the surface ofthe transmissive optical element 58 were not peeled off, and there wasno change in the appearance of the transmissive optical element 58.Moreover, as a result of evaluation concerning infiltration of thedeuterated water into the surface of the transmissive optical element 58in the depth direction in accordance with the secondary ion massspectrometry (SIMS), it was confirmed that the deuterated water did notinfiltrate into the metal film 60.

Example 5

FIG. 44 is a view showing a configuration of a transmissive opticalelement 65 of the Example 5. As shown in FIG. 44, an adhesionreinforcing film 67 is formed by depositing tantalum (Ta) in a thicknessof 10 nm on a substrate of calcium fluoride 66 by use of the sputteringmethod. The adhesion reinforcing layer 67 has a function to improveadhesion between the calcium fluoride 66 and a metal film 68 to beformed on a surface of the adhesion reinforcing layer 67. Here, the filmthickness required for increasing the adhesion is equal to or above 10nm. However, an effect of adhesion can be achieved by the film thicknessin a range from 3 to 5 nm.

Next, the metal film 68 made of gold (Au) functioning as theanti-dissolution film for preventing dissolution in water is formed in athickness of 200 nm on the surface of the adhesion reinforcing film 67by use of the sputtering method.

Here, density of the metal film 67 can be determined by a critical anglein X-ray diffraction. When the film is formed by the sputtering method,packing density of the metal film 67 is equal to or above 97%.Meanwhile, solubility of the metal film 67 to water is equal to or below1 ppt when the film is formed by the sputtering method.

An experiment was performed by use of the transmissive optical element65. As similar to Example 3, a thirty-day water resistance test wasconducted by use of the tester 80 shown in FIG. 42 while a travelingspeed of deuterated water on the transmissive optical element 65 wasbeing set equal to 50 cm/sec. As a result, the films formed on thesurface of the transmissive optical element 65 were not peeled off, andthere was no change in the appearance of the transmissive opticalelement 65. Moreover, as a result of evaluation concerning infiltrationof the deuterated water into the surface of the transmissive opticalelement 65 in the depth direction in accordance with the secondary ionmass spectrometry (SIMS), it was confirmed that the deuterated water didnot infiltrate into the transmissive optical element 65.

Although the sputtering method was used as the film forming method inthe respective examples described above, it is also possible to form theadhesion reinforcing film, the metal film, and the protective film forthe anti-dissolution film by use of the vacuum vapor deposition methodor the CVD method.

Example 6

FIG. 45 is a view showing a configuration of an optical element 50 ofthis example. As shown in FIG. 45, an anti-dissolution film 52 made ofmagnesium fluoride (MgF₂) is formed on a surface 51A on a substrate'sside of an optical member 51 and on a side surface 51B of the opticalmember 51 by use of a wet film forming method, or by spray coating inparticular. Here, the anti-dissolution film 52 made of magnesiumfluoride (MgF₂) is formed in an optical film thickness of 0.65λ (λ=193nm) on the surface 51A on the substrate's side of the optical member 51.Here, the wet film forming method means a film forming method includingthe steps of dispersing a substance intended for forming the film in acertain solvent, coating a film forming surface with the solvent, anddrying and removing the solvent after coating. The solvent used hereinshould only be a solvent that allows uniform dispersion of the intendedsubstance without condensation or precipitation. In particular, asolvent such as alcohol or an organic solvent is used herein.

When forming the magnesium fluoride (MgF₂) film by use of the wet filmforming method, it is preferable to carryout the following three typesof reaction processes.

(i) Hydrofluoric acid/magnesium acetate method

2HF+Mg(CH₃COO)₂→MgF₂+2CH₃COOH

(ii) Hydrofluoric acid/alkoxide method

2HF+Mg(C₂H₅O)₂→MgF₂+2C₂H₅OH

(iii) Trifluoroacetate/alkoxide method

2CF₃COOH+Mg(C₂H₅O)₂→Mg(CF₃COO)₂+2C₂H₅OH

Mg(CF₃COO)₂→thermal decomposition→MgF₂

After adjusting a sol solution in these processes, it is preferable tocarry out either an organothermal process or a hydrothermal process as apretreatment. In this case, it is possible to perform any one of or bothof pressurization and thermal maturation. Details of the above-describedwet film forming methods are disclosed in U.S. Pat. No. 5,835,275 forreference. As for the method of coating the substrate with the solsolution, at least one method is selected from the spin coating method,the dipping method, the meniscus method, the spray coating method, andthe printing method. After coating the substrate with the sol solution,the film is formed by heating and removing the organic matter. Thesurface 51A on the substrate's side and the side surface 51B of theoptical member 51 made of calcium fluoride need to be protected by theformed film without leaving any spaces.

The film formed by use of the wet film forming method has considerablylow mechanical durability as compared to a film formed by a typical dryfilm forming method as represented by the vacuum vapor deposition methodor the sputtering method. Accordingly, it is necessary to heat andanneal the film to improve the mechanical durability. In particular,when the film is formed on the optical member made of calcium fluorideby use of the wet film forming method, there is a risk of surfacedeformation attributable to the linear coefficient of expansion ofcalcium fluoride, or occurrence of cracks on calcium fluoride in anextreme case if the annealing process is conducted by rapidly increasingthe temperature. To avoid such a trouble, it is essential to raise thetemperature at a low rate.

Although magnesium fluoride (MgF₂) is used for the anti-dissolution filmin this example, the present invention is not limited to the foregoing.It is by all means possible to use silicon oxide (SiO₂) formed by thewet film forming method instead.

Example 7

FIG. 46 is a view showing a configuration of an optical element 53 ofthis example. As shown in FIG. 46, an anti-dissolution film 55 made ofsilicon oxide (SiO₂) is formed on a surface 54A on a substrate's side ofan optical member 54 in an optical film thickness of 0.65λ (λ=193 nm) byuse of the ion beam sputtering method. Thereafter, a heated sidedsurface 54B of the optical member 54 is coated with an alkyl ketenedimmer (AKD) solution. When the liquid alkyl ketene dimmer iscrystallized, the alkyl ketene dimmer is formed into a fractal structurethat includes small irregular shapes inside other irregular shapes. Inthis way, the alkyl ketene dimmer is formed into a superhydrophobic filmhaving a contact angle equal to or above 160 degrees.

This phenomenon is understood by the fact that the following extendedYoung's formula holds true assuming that θ_(f) is a contact angle when asubstance having a contact angle θ is formed into a fractal structurehaving the surface area that is r times greater.

$\begin{matrix}{{\cos \; \theta_{f}} = {\frac{r\left( {\gamma_{S} - \gamma_{SL}} \right)}{\gamma_{L}} = {r\mspace{11mu} \cos \; \theta}}} & ({Formula})\end{matrix}$

Here, γ_(S) denotes surface tension of a solid, γ_(L) denotes surfacetension of a liquid, and γ_(SL) denotes interfacial tension between thesolid and the liquid. As shown in this formula, the contact anglebecomes greater when cos θ is positive (θ>90°). In other words, the filmis a more liquid repellent. On the contrary, the contact angle becomessmaller when cos θ is negative (θ<90°). In other words, the film is morewettable to the liquid.

Although alkyl ketene dimmer having the fractal structure is used forthe anti-dissolution film on the side surface, it is also possible toobtain a similar anti-dissolution effect on the side surface by use ofother typical water repellent processes such as a water repellentprocess applying a silane coupling agent (1H, 2H, 2H,2H-perfluorooctyltrichlorosilane). Alternatively, it is also possible toapply a water repellent process using a typical electroless platingmethod.

Results of verification of the optical elements of Example 6 and Example7 will be described below.

Magnesium fluoride (MgF₂) is formed on a bottom surface of a rectangularsolid calcium fluoride optical element as shown in FIG. 47 as theanti-dissolution film by use of the wet film forming method, or by spraycoating in particular. Then, magnesium fluoride (MgF₂) is formed on aside surface of the calcium fluoride optical element as theanti-dissolution film by use of the wet film forming method, or by spraycoating in particular. The anti-dissolution film identical to theanti-dissolution film of Example 6 is formed on an optical element 57shown in FIG. 47. This optical element shown in FIG. 47 is defined as asample 1.

Silicon dioxide (SiO₂) is formed on a bottom surface of a rectangularsolid calcium fluoride optical element as shown in FIG. 48 as theanti-dissolution film by use of the ion beam sputtering method. Then,the alkyl ketene dimmer solution is coated and dried on a side surfaceof the calcium fluoride optical element as the anti-dissolution film.The anti-dissolution film identical to the anti-dissolution film ofExample 7 is formed on an optical element 58 shown in FIG. 48. Thisoptical element shown in FIG. 48 is defined as a sample 2.

Magnesium fluoride (MgF₂) is formed on a bottom surface of a rectangularsolid calcium fluoride optical element as shown in FIG. 49 as theanti-dissolution film by use of the wet film forming method, or by spraycoating in particular. A side surface thereof is uncoated. This opticalelement 59 shown in FIG. 49 is defined as a sample 3 (Reference Example1).

The following experiment was performed by use of the samples 1, 2, and3. FIG. 50 is a view showing a configuration of an experimental device.Pure water 66 at the temperature of 70° C. is put into a tank 64 made ofpolyether ether ketone (PEEK) which is large enough for the volumes ofthe optical elements 57, 58, and 59. A beater 68 made of Teflon(registered trademark) is put into the pure water 66. As shown in FIG.50, the optical elements 57, 58, and 59 are put into the pure water 66so that only the bottom surfaces of the optical elements 57, 58, and 59are soaked in the pure water 66. The tank 64 containing the opticalelements 57, 58, and 59, the pure water 66, and the beater 68 is putinto a constant-temperature tank 70 to maintain a constant temperature.

The tank 64 used herein has a sufficiently large size relative to thevolumes of the optical elements 57, 58, and 59 to reduce a liquid levelchange attributable to evaporation of the pure water 66. Moreover, thebeater 68 is used for maintaining constant solubility even when theoptical elements 57, 58, and 59 dissolve in the pure water 66 andthereby generate a buffer solution. After a lapse of 3 hours whilesoaking the optical elements 57, 58, and 59 in the pure water 66, stepsbetween the bottom surfaces and the side surfaces respectively of theoptical elements 57, 58, and 59 were measured with a step-measurementgauge having resolving power of 0.5 nm.

As shown in FIG. 51, the bottom surfaces and the side surfaces of theoptical element 57 (the sample 1) and the optical element 58 (the sample2) did not dissolve at all. On the contrary, in terms of the opticalelement 59 (the sample 3), the side surface was corroded in an amount ofabout 50 nm. Although the central part of the bottom surface of theoptical element 59 (the sample 3) did not change. However, as shown inFIG. 52, the anti-dissolution film in the periphery of the bottomsurface was partially destroyed due to the corrosion on the sidesurface.

Example 8

FIG. 53 is a view showing a configuration of a transmissive opticalelement 50 of Example 8. As shown in FIG. 53, a silicon dioxide (SiO₂)film 54 is formed in a thickness of 200 nm on a surface of a substrateof calcium fluoride 52 by use of the sputtering method.

Next, a silicon dioxide (SiO₂) film 56 is formed in a thickness of 50 nmby use of the wet film forming method, or by spin coating in particular,on a surface of the silicon dioxide (SiO₂) film 54, which is formed onthe surface of the substrate of calcium fluoride 52 by use of thesputtering method. Specifically, the surface is coated with acommercially available sol-gel silica solution for wet film forming at arotating speed of the substrate in a range from 1000 to 2000 revolutionsper minute. Here, the film thickness of the silicon dioxide (SiO₂) film56 to be formed by the wet film forming method depends on theconcentration and viscosity of the sol-gel silica solution for wet filmforming, the rotating speed of the substrate in the spin coatingprocess, the temperature, humidity, and the like. Accordingly, it isessential to produce an analytical curve concerning the film thicknessof the silicon dioxide (SiO₂) film 56 relative to the concentration andthe viscosity of the sol-gel silica solution for wet film forming by useof the concentration and the viscosity of the sol-gel silica solutionfor wet film forming as parameters. Meanwhile, the film thickness of thesilicon dioxide (SiO₂) film 56 formed by the wet film forming method isset to 50 nm in order to minimize tensile stress on the film. When thefilm thickness of the silicon dioxide (SiO₂) film 56 is set equal to orabove 150 nm, it is necessary to pay attention because cracks may begenerated on the film due to stress relaxation.

Next, the silicon dioxide (SiO₂) film 56 is subjected to an annealingprocess in the air at the temperature of 160° C. for two hours toevaporate alcohol, which is a main solvent of the sol-gel silicasolution for wet film forming, and to sinter the silicon dioxide (SiO₂)film 56 formed by the wet film forming method. The annealing process isperformed on the silicon dioxide (SiO₂) film 56 in the air and theentire substrate of calcium fluoride 52 is evenly heated. Accordingly,no damage or variation in the shape of the surface occurs.

An experiment was performed by use of the transmissive optical element50 with the tester 80 shown in FIG. 42. As shown in FIG. 42, the tester80 includes the sample holder 81, the circulation pump 82, thedeuterated water supply device 83, and the buffer tank 84. One surfaceof the sample holder 81 is open, and the O-ring 85 is provided on theopen surface. The surface of the transmissive optical element 50 wherethe silicon dioxide (SiO₂) films 54 and 56 are formed on is attached tothe open surface of the sample holder 81 and is sealed with the O-ring85. Deuterated water is supplied from the deuterated water supply device83 by use of the circulation pump 82 and is allowed to flow inside thesample holder 81 through the buffer tank 84. Here, the buffer tank 84 isprovided in order to prevent transmission of vibrations of thecirculation pump 82 to the sample holder 81. Moreover, by supplyingdeuterated water (D₂O) instead of pure water (H₂O), it is possible tomeasure an amount of deuterated water infiltrating the surface of thetransmissive optical element 50 in the depth direction after a waterresistance test.

A thirty-day water resistance test was conducted by use of the tester 80while a traveling speed of deuterated water on the transmissive opticalelement 50 was being set equal to 50 cm/sec. As a result, the filmsformed on the surface of the transmissive optical element 50 were notpeeled off, and there was no change in the appearance of thetransmissive optical element 50. Moreover, as a result of evaluationconcerning infiltration of the deuterated water into the surface of thetransmissive optical element 50 in the depth direction in accordancewith the secondary ion mass spectrometry (SIMS), it was confirmed thatthe deuterated water did not infiltrate into the silicon oxide films.

The sputtering method is used as the dry film forming method in Example8. Instead, it is possible to form the film for preventing dissolutionof the transmissive optical element by use of the vacuum vapordeposition method or the CVD method.

Example 9

Next, a transmissive optical element of Embodiment 9 will be described.A magnesium fluoride (MgF₂) film is formed in a thickness of 70 nm on aheated calcium fluoride substrate by use of the vacuum vapor depositionmethod. Here, when heating calcium fluoride to form the magnesiumfluoride (MgF₂) film in a vacuum, the entire calcium fluoride substrateshould be evenly heated in order to avoid damage or variation in theshape of the surface attributable to a thermal impact on the calciumfluoride substrate having a high thermal expansion coefficient.Moreover, when heating or cooling the calcium fluoride substrate, it isnecessary to perform heating or cooling at a low rate.

Subsequently, a silicon dioxide (SiO₂) film is formed in a thickness of50 nm by use of the wet film forming method, or by spin coating inparticular, on a surface of the magnesium fluoride (MgF₂) film, which isformed on the surface of the substrate of calcium fluoride by use of thevacuum vapor deposition method. Specifically, the surface is coated witha commercially available sol-gel silica solution for wet film forming ata rotating speed of the substrate in a range from 1000 to 2000revolutions per minute. Here, the film thickness of the silicon dioxide(SiO₂) film to be formed by the wet film forming method depends on theconcentration and viscosity of the sol-gel silica solution for wet filmforming, the rotating speed of the substrate in the spin coatingprocess, the temperature, humidity, and the like. Accordingly, it isessential to produce the analytical curve concerning the film thicknessof the silicon dioxide (SiO₂) film relative to the concentration and theviscosity of the sol-gel silica solution for wet film forming by use ofthe concentration and the viscosity of the sol-gel silica solution forwet film forming as parameters. Meanwhile, the film thickness of thesilicon dioxide (SiO₂) film formed by the wet film forming method is setto 50 nm in order to minimize tensile stress on the film. When the filmthickness of the silicon dioxide (SiO₂) film is set equal to or above150 nm, it is necessary to pay attention because cracks may be generatedon the film due to stress relaxation.

Next, the silicon dioxide (SiO₂) film is subjected to the annealingprocess in the air at the temperature of 160° C. for two hours toevaporate alcohol, which is the main solvent of the sol-gel silicasolution for wet film forming, and to sinter the silicon dioxide (SiO₂)film formed by the wet film forming method. The annealing process isperformed in the air and the entire substrate of calcium fluoride isevenly heated. Accordingly, no damage or variation in the shape of thesurface occurs.

An experiment was performed by use of the transmissive optical elementof Example 9. As similar to Example 8, a thirty-day water resistancetest was conducted by use of the tester 80 shown in FIG. 42 whilesetting a traveling speed of deuterated water on the transmissiveoptical element of Example 9 equal to 50 cm/sec. As a result, the filmsformed on the surface of the transmissive optical element were notpeeled off, and there was no change in the appearance of thetransmissive optical element. Moreover, as a result of evaluationconcerning infiltration of the deuterated water into the surface of thetransmissive optical element in the depth direction in accordance withthe secondary ion mass spectrometry (SIMS), it was confirmed that thedeuterated water did not infiltrate into the silicon oxide film.

The vacuum vapor deposition method was used as the dry film formingmethod in Example 9. Instead, it is possible to form the film forpreventing dissolution of the transmissive optical element by use of thesputtering method or the CVD method.

Example 10

FIG. 54 is a view showing a configuration of a transmissive opticalelement 58 of Example 10, which has an anti-reflection effect at acentral wavelength of 193.4 nm. As shown in FIG. 54, a lanthanumfluoride (LaF₃) film 60 as a first layer, a magnesium fluoride (MgF₂)film 61 as a second layer, and a lanthanum fluoride (LaF₃) film 62 as athird layer are formed on a substrate made of calcium fluoride (CaF₂) 59heated by resistance heating in accordance with the vacuum vapordeposition method. Subsequently, a silicon dioxide (SiO₂) film 63 as afirst film constituting part of a fourth layer is formed in an opticalthickness of 0.08λ by electron gun heating in accordance with the vacuumvapor deposition method. Then, the calcium fluoride 59 including thefirst layer to part of the fourth layer is taken out of a vacuumchamber. Thereafter, a silicon dioxide (SiO₂) film 64 as a second filmconstituting part of the fourth layer is formed in an optical thicknessof 0.04λ by the wet film forming method, or by spin coating inparticular. Next, the silicon dioxide (SiO₂) film 64 is subjected to theannealing process in the air at the temperature of 160° C. for two hoursto sinter the silicon dioxide (SiO₂) film 64 formed by the wet filmforming method. Refractive indices n relative to a light flux having thecentral wavelength of 193.4 nm, and optical film thicknesses nd relativeto the light flux having the central wavelength of 193.4 concerning thesubstrate, oxide films, and the like constituting the transmissiveoptical element 58 will be listed below:

Substrate: CaF₂ (n=1.50);First layer: LaF₃ (n=1.69, nd=0.60);Second layer: MgF₂ (n=1.43, nd=0.66);Third layer: LaF₃ (n=1.69, nd=0.52);Fourth layer: SiO₂ (n=1.55, nd=0.12); andMedium: H₂O (n=1.44)

An experiment was performed by use of the transmissive optical element58. As similar to Example 8, a thirty-day water resistance test wasconducted by use of the tester 80 shown in FIG. 42 while a travelingspeed of deuterated water on the transmissive optical element 58 wasbeing equal to 50 cm/sec. As a result, the films formed on the surfaceof the transmissive optical element 58 were not peeled off, and therewas no change in the appearance of the transmissive optical element 58.Moreover, as a result of evaluation concerning infiltration of thedeuterated water into the surface of the transmissive optical element 58in the depth direction in accordance with the secondary ion massspectrometry (SIMS), it was confirmed that the deuterated water did notinfiltrate into the films.

Example 11

FIG. 55 is a view showing a configuration of a transmissive opticalelement 65 of Example 11. As shown in FIG. 55, a surface treatment isperformed on a substrate of calcium fluoride 66. Specifically, thesubstrate of calcium fluoride 66 is polished with a #2000 grind stone toincrease surface roughness and the surface area thereof. Then, thesubstrate of calcium fluoride 66, which is subjected to the surfacetreatment by polishing with the grind stone, is coated with a silicondioxide (SiO₂) film 67, which serves as an oxide anti-dissolution film,in a thickness of 100 nm by the wet film forming method, or by spincoating in particular. Next, the silicon dioxide (SiO₂) film 67 issubjected to the annealing process in the air at the temperature of 160°C. for two hours to sinter the silicon dioxide (SiO₂) film 67 formed bythe wet film forming method.

An experiment was performed by use of the transmissive optical element65. As similar to Example 8, a thirty-day water resistance test wasconducted by use of the tester 80 shown in FIG. 42 while setting atraveling speed of deuterated water on the transmissive optical element65 equal to 50 cm/sec. As a result, the films formed on the surface ofthe transmissive optical element 65 were not peeled off, and there wasno change in the appearance of the transmissive optical element 65.Moreover, as a result of evaluation concerning infiltration of thedeuterated water into the surface of the transmissive optical element 65in the depth direction in accordance with the secondary ion massspectrometry (SIMS), it was confirmed that the deuterated water did notinfiltrate into the films.

Reference Example 2

FIG. 56 is a view showing a configuration of a transmissive opticalelement 73 of Reference Example 2, which has an anti-reflection effectat a central wavelength of 193.4 nm. As shown in FIG. 56, a lanthanumfluoride (LaF₃) film 75 as a first layer, a magnesium fluoride (MgF₂)film 76 as a second layer, and a lanthanum fluoride (LaF₃) film 77 as athird layer are formed on a substrate made of calcium fluoride 74 heatedby resistance heating in accordance with the vacuum vapor depositionmethod. Subsequently, a silicon dioxide (SiO₂) film 78 as a fourth layeris formed by electron gun heating in accordance with the vacuum vapordeposition method.

Here, the lanthanum fluoride (LaF₃) film 75 as the first layer, themagnesium fluoride (MgF₂) film 76 as the second layer, and the lanthanumfluoride (LaF₃) film 77 as the third layer collectively constituting thetransmissive optical element 73 of Reference example 2 have the samerefractive indices n and the same optical film thicknesses nd relativeto the light flux having the central wavelength of 193.4 nm as those ofthe lanthanum fluoride (LaF₃) film 60 as the first layer, the magnesiumfluoride (MgF₂) film 61 as the second layer, and the lanthanum fluoride(LaF₃) film 62 as the third layer collectively constituting thetransmissive optical element 58 of Example 10. Meanwhile, the silicondioxide (SiO₂) film 78 as the fourth layer has the same refractive indexn and the same optical film thickness nd relative to the light fluxhaving the central wavelength of 193.4 nm as those of the silicondioxide (SiO₂) film 63 and the silicon dioxide (SiO₂) film 64constituting the fourth layer of Example 9.

An experiment was performed by use of the transmissive optical element73. As similar to Example 8, a thirty-day water resistance test wasconducted by use of the tester 80 shown in FIG. 42 while setting atraveling speed of deuterated water on the transmissive optical element73 equal to 50 cm/sec. After the water resistance test, infiltration ofthe deuterated water into the surface of the transmissive opticalelement 73 in the depth direction was evaluated in accordance with thesecondary ion mass spectrometry (SIMS). As a result, deuterated waterwas detected from the inside of the silicon dioxide (SiO₂) film 78 asthe fourth layer formed on the surface of the transmissive opticalelement 73, and in the vicinity of the interface with the lanthanumfluoride (LaF₃) film 77 as the third layer.

In comparison with the transmissive optical element of Reference example2, the transmissive optical element of Embodiment 10 can preventinfiltration of and corrosion by deuterated water without changing theoptical characteristic thereof. FIG. 57 is a graph showingangle-reflectivity characteristics when light from a medium (pure water)is incident on the transmissive optical elements of Example 10 andReference Example 2. A solid line 90 in FIG. 57 indicatesangle-reflectivity characteristics of S polarization components of thelight incident on the transmissive optical elements of Example 10 andReference Example 2. Meanwhile, a dashed line 91 in FIG. 57 indicatesangle-reflectivity characteristics of P polarization components of thelight incident on the transmissive optical elements of Example 10 andReference Example 2. As shown in FIG. 57, the angle-reflectivitycharacteristics of the S polarization components and the P polarizationcomponents of the light incident on the transmissive optical element areequal between Example 10 and Reference Example 2. Accordingly, it isapparent that the transmissive optical elements of Example 10 andReference Example 2 have the identical optical characteristics.

INDUSTRIAL APPLICABILITY

As described above, the present invention can provide an optical elementconfigured to avoid a tip portion of a projection optical system frombeing corroded by a liquid when the liquid immersion method is applied.Therefore, according to the present invention, it is possible to providean exposure apparatus which is capable of sufficiently preventingdissolution of the optical element and maintaining optical performanceof the projection optical system over a long time period.

1. An optical element to be used for an exposure apparatus configured toilluminate a mask with an exposure light beam for transferring a patternon the mask onto a substrate through a projection optical system and tointerpose a given liquid in a space between a surface of the substrateand the projection optical system, the optical element comprising: afirst anti-dissolution member provided on a surface of a transmissiveoptical element on the substrate's side of the projection opticalsystem.
 2. The optical element according to claim 1, wherein the firstanti-dissolution member comprises a thin plate having a protectivefunction to protect the optical element against the liquid and ananti-reflection function to prevent reflection of the exposure lightbeam, wherein the thin plate is detachably joined to a surface of theoptical element.
 3. The optical element according to claim 2, whereinthe thin plate is joined to the surface of the optical element byoptical contact, and mean reflectance of the thin plate is equal to orbelow 2% when an exit angle of the exposure light beam is set to 50degrees.
 4. The optical element according to claim 2, wherein the thinplate is made of at least one selected from the group consisting of afluoride, an oxide, and resin.
 5. The optical element according to claim2, wherein the thin plate is at least one selected from the groupconsisting of a fused silica thin plate, a magnesium fluoride thinplate, a calcium fluoride thin plate, and a polytetrafluoroethylene thinplate.
 6. An exposure apparatus configured to illuminate a mask with anexposure light beam for transferring a pattern on the mask onto asubstrate through a projection optical system and to interpose a givenliquid in a space between a surface of the substrate and the projectionoptical system, the exposure apparatus comprising: a firstanti-dissolution member provided on a surface of a transmissive opticalelement on the substrate's side of the projection optical system.
 7. Theexposure apparatus according to claim 6, wherein the firstanti-dissolution member comprises a thin plate having a protectivefunction to protect the optical element against the liquid and ananti-reflection function to prevent reflection of the exposure lightbeam, and the thin plate is detachably joined to a surface of theoptical element.